Справочник языка Zig

const std = @import("std");

pub fn main() !void {
    const stdout = std.io.getStdOut().writer();
    try stdout.print("Hello, {s}!\n", .{"world"});
}

$ zig build-exe hello.zig
$ ./hello
Hello, world!

const std = @import("std");

pub fn main() void {
    std.debug.print("Hello, world!\n", .{});
}

$ zig build-exe hello_again.zig
$ ./hello_again
Hello, world!

zig test -femit-docs main.zig

const print = @import("std").debug.print;

pub fn main() void {
    // Comments in Zig start with "//" and end at the next LF byte (end of line).
    // The line below is a comment and won't be executed.

    //print("Hello?", .{});

    print("Hello, world!\n", .{}); // another comment
}

$ zig build-exe comments.zig
$ ./comments
Hello, world!

/// A structure for storing a timestamp, with nanosecond precision (this is a
/// multiline doc comment).
const Timestamp = struct {
    /// The number of seconds since the epoch (this is also a doc comment).
    seconds: i64, // signed so we can represent pre-1970 (not a doc comment)
    /// The number of nanoseconds past the second (doc comment again).
    nanos: u32,

    /// Returns a `Timestamp` struct representing the Unix epoch; that is, the
    /// moment of 1970 Jan 1 00:00:00 UTC (this is a doc comment too).
    pub fn unixEpoch() Timestamp {
        return Timestamp{
            .seconds = 0,
            .nanos = 0,
        };
    }
};

/// doc-comment
//! top-level doc-comment
const std = @import("std");

$ zig build-obj invalid_doc-comment.zig
doc/langref/invalid_doc-comment.zig:1:16: error: expected type expression, found 'a document comment'
/// doc-comment
               ^

pub fn main() void {}

/// End of file

$ zig build-obj unattached_doc-comment.zig
doc/langref/unattached_doc-comment.zig:3:1: error: unattached documentation comment
/// End of file
^~~~~~~~~~~~~~~

//! This module provides functions for retrieving the current date and
//! time with varying degrees of precision and accuracy. It does not
//! depend on libc, but will use functions from it if available.

const S = struct {
    //! Top level comments are allowed inside a container other than a module,
    //! but it is not very useful.  Currently, when producing the package
    //! documentation, these comments are ignored.
};

// Top-level declarations are order-independent:
const print = std.debug.print;
const std = @import("std");
const os = std.os;
const assert = std.debug.assert;

pub fn main() void {
    // integers
    const one_plus_one: i32 = 1 + 1;
    print("1 + 1 = {}\n", .{one_plus_one});

    // floats
    const seven_div_three: f32 = 7.0 / 3.0;
    print("7.0 / 3.0 = {}\n", .{seven_div_three});

    // boolean
    print("{}\n{}\n{}\n", .{
        true and false,
        true or false,
        !true,
    });

    // optional
    var optional_value: ?[]const u8 = null;
    assert(optional_value == null);

    print("\noptional 1\ntype: {}\nvalue: {?s}\n", .{
        @TypeOf(optional_value), optional_value,
    });

    optional_value = "hi";
    assert(optional_value != null);

    print("\noptional 2\ntype: {}\nvalue: {?s}\n", .{
        @TypeOf(optional_value), optional_value,
    });

    // error union
    var number_or_error: anyerror!i32 = error.ArgNotFound;

    print("\nerror union 1\ntype: {}\nvalue: {!}\n", .{
        @TypeOf(number_or_error),
        number_or_error,
    });

    number_or_error = 1234;

    print("\nerror union 2\ntype: {}\nvalue: {!}\n", .{
        @TypeOf(number_or_error), number_or_error,
    });
}

$ zig build-exe values.zig
$ ./values
1 + 1 = 2
7.0 / 3.0 = 2.3333333e0
false
true
false

optional 1
type: ?[]const u8
value: null

optional 2
type: ?[]const u8
value: hi

error union 1
type: anyerror!i32
value: error.ArgNotFound

error union 2
type: anyerror!i32
value: 1234

const print = @import("std").debug.print;
const mem = @import("std").mem; // will be used to compare bytes

pub fn main() void {
    const bytes = "hello";
    print("{}\n", .{@TypeOf(bytes)}); // *const [5:0]u8
    print("{d}\n", .{bytes.len}); // 5
    print("{c}\n", .{bytes[1]}); // 'e'
    print("{d}\n", .{bytes[5]}); // 0
    print("{}\n", .{'e' == '\x65'}); // true
    print("{d}\n", .{'\u{1f4a9}'}); // 128169
    print("{d}\n", .{'💯'}); // 128175
    print("{u}\n", .{'⚡'});
    print("{}\n", .{mem.eql(u8, "hello", "h\x65llo")}); // true
    print("{}\n", .{mem.eql(u8, "💯", "\xf0\x9f\x92\xaf")}); // also true
    const invalid_utf8 = "\xff\xfe"; // non-UTF-8 strings are possible with \xNN notation.
    print("0x{x}\n", .{invalid_utf8[1]}); // indexing them returns individual bytes...
    print("0x{x}\n", .{"💯"[1]}); // ...as does indexing part-way through non-ASCII characters
}

$ zig build-exe string_literals.zig
$ ./string_literals
*const [5:0]u8
5
e
0
true
128169
128175
⚡
true
true
0xfe
0x9f

const hello_world_in_c =
    \\#include <stdio.h>
    \\
    \\int main(int argc, char **argv) {
    \\    printf("hello world\n");
    \\    return 0;
    \\}
;

const x = 1234;

fn foo() void {
    // It works at file scope as well as inside functions.
    const y = 5678;

    // Once assigned, an identifier cannot be changed.
    y += 1;
}

pub fn main() void {
    foo();
}

$ zig build-exe constant_identifier_cannot_change.zig
/home/andy/src/zig/doc/langref/constant_identifier_cannot_change.zig:8:7: error: cannot assign to constant
    y += 1;
    ~~^~~~
referenced by:
    main: /home/andy/src/zig/doc/langref/constant_identifier_cannot_change.zig:12:5
    callMain: /home/andy/src/zig/lib/std/start.zig:514:17
    remaining reference traces hidden; use '-freference-trace' to see all reference traces

const print = @import("std").debug.print;

pub fn main() void {
    var y: i32 = 5678;

    y += 1;

    print("{d}", .{y});
}

$ zig build-exe mutable_var.zig
$ ./mutable_var
5679

pub fn main() void {
    var x: i32;

    x = 1;
}

$ zig build-exe var_must_be_initialized.zig
/home/andy/src/zig/doc/langref/var_must_be_initialized.zig:2:15: error: expected '=', found ';'
    var x: i32;
              ^

const print = @import("std").debug.print;

pub fn main() void {
    var x: i32 = undefined;
    x = 1;
    print("{d}", .{x});
}

$ zig build-exe assign_undefined.zig
$ ./assign_undefined
1

const std = @import("std");

test "expect addOne adds one to 41" {

    // The Standard Library contains useful functions to help create tests.
    // `expect` is a function that verifies its argument is true.
    // It will return an error if its argument is false to indicate a failure.
    // `try` is used to return an error to the test runner to notify it that the test failed.
    try std.testing.expect(addOne(41) == 42);
}

test addOne {
    // A test name can also be written using an identifier.
    // This is a doctest, and serves as documentation for `addOne`.
    try std.testing.expect(addOne(41) == 42);
}

/// The function `addOne` adds one to the number given as its argument.
fn addOne(number: i32) i32 {
    return number + 1;
}

$ zig test testing_introduction.zig
1/2 testing_introduction.test.expect addOne adds one to 41...OK
2/2 testing_introduction.decltest.addOne...OK
All 2 tests passed.

const std = @import("std");

test "expect this to fail" {
    try std.testing.expect(false);
}

test "expect this to succeed" {
    try std.testing.expect(true);
}

$ zig test testing_failure.zig
1/2 testing_failure.test.expect this to fail...FAIL (TestUnexpectedResult)
/home/andy/src/zig/lib/std/testing.zig:540:14: 0x103ce3f in expect (test)
    if (!ok) return error.TestUnexpectedResult;
             ^
/home/andy/src/zig/doc/langref/testing_failure.zig:4:5: 0x103cf55 in test.expect this to fail (test)
    try std.testing.expect(false);
    ^
2/2 testing_failure.test.expect this to succeed...OK
1 passed; 0 skipped; 1 failed.
error: the following test command failed with exit code 1:
/home/andy/src/zig/.zig-cache/o/054f0b6f088824f384d1b6c648523593/test

test "this will be skipped" {
    return error.SkipZigTest;
}

$ zig test testing_skip.zig
1/1 testing_skip.test.this will be skipped...SKIP
0 passed; 1 skipped; 0 failed.

const std = @import("std");

test "detect leak" {
    var list = std.ArrayList(u21).init(std.testing.allocator);
    // missing `defer list.deinit();`
    try list.append('☔');

    try std.testing.expect(list.items.len == 1);
}

$ zig test testing_detect_leak.zig
1/1 testing_detect_leak.test.detect leak...OK
[gpa] (err): memory address 0x7fdbea69e000 leaked:
/home/andy/src/zig/lib/std/array_list.zig:457:67: 0x104f76e in ensureTotalCapacityPrecise (test)
                const new_memory = try self.allocator.alignedAlloc(T, alignment, new_capacity);
                                                                  ^
/home/andy/src/zig/lib/std/array_list.zig:434:51: 0x1045610 in ensureTotalCapacity (test)
            return self.ensureTotalCapacityPrecise(better_capacity);
                                                  ^
/home/andy/src/zig/lib/std/array_list.zig:483:41: 0x1041fe0 in addOne (test)
            try self.ensureTotalCapacity(newlen);
                                        ^
/home/andy/src/zig/lib/std/array_list.zig:262:49: 0x103ef2d in append (test)
            const new_item_ptr = try self.addOne();
                                                ^
/home/andy/src/zig/doc/langref/testing_detect_leak.zig:6:20: 0x103d172 in test.detect leak (test)
    try list.append('☔');
                   ^
/home/andy/src/zig/lib/compiler/test_runner.zig:157:25: 0x104c6a0 in mainTerminal (test)
        if (test_fn.func()) |_| {
                        ^
/home/andy/src/zig/lib/compiler/test_runner.zig:37:28: 0x10428bb in main (test)
        return mainTerminal();
                           ^
/home/andy/src/zig/lib/std/start.zig:514:22: 0x103f429 in posixCallMainAndExit (test)
            root.main();
                     ^
/home/andy/src/zig/lib/std/start.zig:266:5: 0x103ef91 in _start (test)
    asm volatile (switch (native_arch) {
    ^

All 1 tests passed.
1 errors were logged.
1 tests leaked memory.
error: the following test command failed with exit code 1:
/home/andy/src/zig/.zig-cache/o/4a17198138bf81bcfabd5652b0d6be24/test

const std = @import("std");
const builtin = @import("builtin");
const expect = std.testing.expect;

test "builtin.is_test" {
    try expect(isATest());
}

fn isATest() bool {
    return builtin.is_test;
}

$ zig test testing_detect_test.zig
1/1 testing_detect_test.test.builtin.is_test...OK
All 1 tests passed.

const std = @import("std");

test "expectEqual demo" {
    const expected: i32 = 42;
    const actual = 42;

    // The first argument to `expectEqual` is the known, expected, result.
    // The second argument is the result of some expression.
    // The actual's type is casted to the type of expected.
    try std.testing.expectEqual(expected, actual);
}

test "expectError demo" {
    const expected_error = error.DemoError;
    const actual_error_union: anyerror!void = error.DemoError;

    // `expectError` will fail when the actual error is different than
    // the expected error.
    try std.testing.expectError(expected_error, actual_error_union);
}

$ zig test testing_namespace.zig
1/2 testing_namespace.test.expectEqual demo...OK
2/2 testing_namespace.test.expectError demo...OK
All 2 tests passed.

const @"identifier with spaces in it" = 0xff;
const @"1SmallStep4Man" = 112358;

const c = @import("std").c;
pub extern "c" fn @"error"() void;
pub extern "c" fn @"fstat$INODE64"(fd: c.fd_t, buf: *c.Stat) c_int;

const Color = enum {
    red,
    @"really red",
};
const color: Color = .@"really red";

var y: i32 = add(10, x);
const x: i32 = add(12, 34);

test "container level variables" {
    try expect(x == 46);
    try expect(y == 56);
}

fn add(a: i32, b: i32) i32 {
    return a + b;
}

const std = @import("std");
const expect = std.testing.expect;

$ zig test test_container_level_variables.zig
1/1 test_container_level_variables.test.container level variables...OK
All 1 tests passed.

const std = @import("std");
const expect = std.testing.expect;

test "namespaced container level variable" {
    try expect(foo() == 1235);
    try expect(foo() == 1236);
}

const S = struct {
    var x: i32 = 1234;
};

fn foo() i32 {
    S.x += 1;
    return S.x;
}

$ zig test test_namespaced_container_level_variable.zig
1/1 test_namespaced_container_level_variable.test.namespaced container level variable...OK
All 1 tests passed.

const std = @import("std");
const expect = std.testing.expect;

test "static local variable" {
    try expect(foo() == 1235);
    try expect(foo() == 1236);
}

fn foo() i32 {
    const S = struct {
        var x: i32 = 1234;
    };
    S.x += 1;
    return S.x;
}

$ zig test test_static_local_variable.zig
1/1 test_static_local_variable.test.static local variable...OK
All 1 tests passed.

const std = @import("std");
const assert = std.debug.assert;

threadlocal var x: i32 = 1234;

test "thread local storage" {
    const thread1 = try std.Thread.spawn(.{}, testTls, .{});
    const thread2 = try std.Thread.spawn(.{}, testTls, .{});
    testTls();
    thread1.join();
    thread2.join();
}

fn testTls() void {
    assert(x == 1234);
    x += 1;
    assert(x == 1235);
}

$ zig test test_thread_local_variables.zig
1/1 test_thread_local_variables.test.thread local storage...OK
All 1 tests passed.

const std = @import("std");
const expect = std.testing.expect;

test "comptime vars" {
    var x: i32 = 1;
    comptime var y: i32 = 1;

    x += 1;
    y += 1;

    try expect(x == 2);
    try expect(y == 2);

    if (y != 2) {
        // This compile error never triggers because y is a comptime variable,
        // and so `y != 2` is a comptime value, and this if is statically evaluated.
        @compileError("wrong y value");
    }
}

$ zig test test_comptime_variables.zig
1/1 test_comptime_variables.test.comptime vars...OK
All 1 tests passed.

const decimal_int = 98222;
const hex_int = 0xff;
const another_hex_int = 0xFF;
const octal_int = 0o755;
const binary_int = 0b11110000;

// underscores may be placed between two digits as a visual separator
const one_billion = 1_000_000_000;
const binary_mask = 0b1_1111_1111;
const permissions = 0o7_5_5;
const big_address = 0xFF80_0000_0000_0000;

fn divide(a: i32, b: i32) i32 {
    return a / b;
}

const floating_point = 123.0E+77;
const another_float = 123.0;
const yet_another = 123.0e+77;

const hex_floating_point = 0x103.70p-5;
const another_hex_float = 0x103.70;
const yet_another_hex_float = 0x103.70P-5;

// underscores may be placed between two digits as a visual separator
const lightspeed = 299_792_458.000_000;
const nanosecond = 0.000_000_001;
const more_hex = 0x1234_5678.9ABC_CDEFp-10;

const std = @import("std");

const inf = std.math.inf(f32);
const negative_inf = -std.math.inf(f64);
const nan = std.math.nan(f128);

const std = @import("std");
const big = @as(f64, 1 << 40);

export fn foo_strict(x: f64) f64 {
    return x + big - big;
}

export fn foo_optimized(x: f64) f64 {
    @setFloatMode(.optimized);
    return x + big - big;
}

$ zig build-obj float_mode_obj.zig -O ReleaseFast

const print = @import("std").debug.print;

extern fn foo_strict(x: f64) f64;
extern fn foo_optimized(x: f64) f64;

pub fn main() void {
    const x = 0.001;
    print("optimized = {}\n", .{foo_optimized(x)});
    print("strict = {}\n", .{foo_strict(x)});
}

const expect = @import("std").testing.expect;
const assert = @import("std").debug.assert;
const mem = @import("std").mem;

// array literal
const message = [_]u8{ 'h', 'e', 'l', 'l', 'o' };

// alternative initialization using result location
const alt_message: [5]u8 = .{ 'h', 'e', 'l', 'l', 'o' };

comptime {
    assert(mem.eql(u8, &message, &alt_message));
}

// get the size of an array
comptime {
    assert(message.len == 5);
}

// A string literal is a single-item pointer to an array.
const same_message = "hello";

comptime {
    assert(mem.eql(u8, &message, same_message));
}

test "iterate over an array" {
    var sum: usize = 0;
    for (message) |byte| {
        sum += byte;
    }
    try expect(sum == 'h' + 'e' + 'l' * 2 + 'o');
}

// modifiable array
var some_integers: [100]i32 = undefined;

test "modify an array" {
    for (&some_integers, 0..) |*item, i| {
        item.* = @intCast(i);
    }
    try expect(some_integers[10] == 10);
    try expect(some_integers[99] == 99);
}

// array concatenation works if the values are known
// at compile time
const part_one = [_]i32{ 1, 2, 3, 4 };
const part_two = [_]i32{ 5, 6, 7, 8 };
const all_of_it = part_one ++ part_two;
comptime {
    assert(mem.eql(i32, &all_of_it, &[_]i32{ 1, 2, 3, 4, 5, 6, 7, 8 }));
}

// remember that string literals are arrays
const hello = "hello";
const world = "world";
const hello_world = hello ++ " " ++ world;
comptime {
    assert(mem.eql(u8, hello_world, "hello world"));
}

// ** does repeating patterns
const pattern = "ab" ** 3;
comptime {
    assert(mem.eql(u8, pattern, "ababab"));
}

// initialize an array to zero
const all_zero = [_]u16{0} ** 10;

comptime {
    assert(all_zero.len == 10);
    assert(all_zero[5] == 0);
}

// use compile-time code to initialize an array
var fancy_array = init: {
    var initial_value: [10]Point = undefined;
    for (&initial_value, 0..) |*pt, i| {
        pt.* = Point{
            .x = @intCast(i),
            .y = @intCast(i * 2),
        };
    }
    break :init initial_value;
};
const Point = struct {
    x: i32,
    y: i32,
};

test "compile-time array initialization" {
    try expect(fancy_array[4].x == 4);
    try expect(fancy_array[4].y == 8);
}

// call a function to initialize an array
var more_points = [_]Point{makePoint(3)} ** 10;
fn makePoint(x: i32) Point {
    return Point{
        .x = x,
        .y = x * 2,
    };
}
test "array initialization with function calls" {
    try expect(more_points[4].x == 3);
    try expect(more_points[4].y == 6);
    try expect(more_points.len == 10);
}

$ zig test test_arrays.zig
1/4 test_arrays.test.iterate over an array...OK
2/4 test_arrays.test.modify an array...OK
3/4 test_arrays.test.compile-time array initialization...OK
4/4 test_arrays.test.array initialization with function calls...OK
All 4 tests passed.

const std = @import("std");
const expect = std.testing.expect;

const mat4x4 = [4][4]f32{
    [_]f32{ 1.0, 0.0, 0.0, 0.0 },
    [_]f32{ 0.0, 1.0, 0.0, 1.0 },
    [_]f32{ 0.0, 0.0, 1.0, 0.0 },
    [_]f32{ 0.0, 0.0, 0.0, 1.0 },
};
test "multidimensional arrays" {
    // Access the 2D array by indexing the outer array, and then the inner array.
    try expect(mat4x4[1][1] == 1.0);

    // Here we iterate with for loops.
    for (mat4x4, 0..) |row, row_index| {
        for (row, 0..) |cell, column_index| {
            if (row_index == column_index) {
                try expect(cell == 1.0);
            }
        }
    }
}

$ zig test test_multidimensional_arrays.zig
1/1 test_multidimensional_arrays.test.multidimensional arrays...OK
All 1 tests passed.

const std = @import("std");
const expect = std.testing.expect;

test "0-terminated sentinel array" {
    const array = [_:0]u8{ 1, 2, 3, 4 };

    try expect(@TypeOf(array) == [4:0]u8);
    try expect(array.len == 4);
    try expect(array[4] == 0);
}

test "extra 0s in 0-terminated sentinel array" {
    // The sentinel value may appear earlier, but does not influence the compile-time 'len'.
    const array = [_:0]u8{ 1, 0, 0, 4 };

    try expect(@TypeOf(array) == [4:0]u8);
    try expect(array.len == 4);
    try expect(array[4] == 0);
}

$ zig test test_null_terminated_array.zig
1/2 test_null_terminated_array.test.0-terminated sentinel array...OK
2/2 test_null_terminated_array.test.extra 0s in 0-terminated sentinel array...OK
All 2 tests passed.

const std = @import("std");
const expectEqual = std.testing.expectEqual;

test "Basic vector usage" {
    // Vectors have a compile-time known length and base type.
    const a = @Vector(4, i32){ 1, 2, 3, 4 };
    const b = @Vector(4, i32){ 5, 6, 7, 8 };

    // Math operations take place element-wise.
    const c = a + b;

    // Individual vector elements can be accessed using array indexing syntax.
    try expectEqual(6, c[0]);
    try expectEqual(8, c[1]);
    try expectEqual(10, c[2]);
    try expectEqual(12, c[3]);
}

test "Conversion between vectors, arrays, and slices" {
    // Vectors and fixed-length arrays can be automatically assigned back and forth
    const arr1: [4]f32 = [_]f32{ 1.1, 3.2, 4.5, 5.6 };
    const vec: @Vector(4, f32) = arr1;
    const arr2: [4]f32 = vec;
    try expectEqual(arr1, arr2);

    // You can also assign from a slice with comptime-known length to a vector using .*
    const vec2: @Vector(2, f32) = arr1[1..3].*;

    const slice: []const f32 = &arr1;
    var offset: u32 = 1; // var to make it runtime-known
    _ = &offset; // suppress 'var is never mutated' error
    // To extract a comptime-known length from a runtime-known offset,
    // first extract a new slice from the starting offset, then an array of
    // comptime-known length
    const vec3: @Vector(2, f32) = slice[offset..][0..2].*;
    try expectEqual(slice[offset], vec2[0]);
    try expectEqual(slice[offset + 1], vec2[1]);
    try expectEqual(vec2, vec3);
}

$ zig test test_vector.zig
1/2 test_vector.test.Basic vector usage...OK
2/2 test_vector.test.Conversion between vectors, arrays, and slices...OK
All 2 tests passed.

const expect = @import("std").testing.expect;

test "address of syntax" {
    // Get the address of a variable:
    const x: i32 = 1234;
    const x_ptr = &x;

    // Dereference a pointer:
    try expect(x_ptr.* == 1234);

    // When you get the address of a const variable, you get a const single-item pointer.
    try expect(@TypeOf(x_ptr) == *const i32);

    // If you want to mutate the value, you'd need an address of a mutable variable:
    var y: i32 = 5678;
    const y_ptr = &y;
    try expect(@TypeOf(y_ptr) == *i32);
    y_ptr.* += 1;
    try expect(y_ptr.* == 5679);
}

test "pointer array access" {
    // Taking an address of an individual element gives a
    // single-item pointer. This kind of pointer
    // does not support pointer arithmetic.
    var array = [_]u8{ 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
    const ptr = &array[2];
    try expect(@TypeOf(ptr) == *u8);

    try expect(array[2] == 3);
    ptr.* += 1;
    try expect(array[2] == 4);
}

$ zig test test_single_item_pointer.zig
1/2 test_single_item_pointer.test.address of syntax...OK
2/2 test_single_item_pointer.test.pointer array access...OK
All 2 tests passed.

const expect = @import("std").testing.expect;

test "pointer arithmetic with many-item pointer" {
    const array = [_]i32{ 1, 2, 3, 4 };
    var ptr: [*]const i32 = &array;

    try expect(ptr[0] == 1);
    ptr += 1;
    try expect(ptr[0] == 2);

    // slicing a many-item pointer without an end is equivalent to
    // pointer arithmetic: `ptr[start..] == ptr + start`
    try expect(ptr[1..] == ptr + 1);
}

test "pointer arithmetic with slices" {
    var array = [_]i32{ 1, 2, 3, 4 };
    var length: usize = 0; // var to make it runtime-known
    _ = &length; // suppress 'var is never mutated' error
    var slice = array[length..array.len];

    try expect(slice[0] == 1);
    try expect(slice.len == 4);

    slice.ptr += 1;
    // now the slice is in an bad state since len has not been updated

    try expect(slice[0] == 2);
    try expect(slice.len == 4);
}

$ zig test test_pointer_arithmetic.zig
1/2 test_pointer_arithmetic.test.pointer arithmetic with many-item pointer...OK
2/2 test_pointer_arithmetic.test.pointer arithmetic with slices...OK
All 2 tests passed.

const expect = @import("std").testing.expect;

test "pointer slicing" {
    var array = [_]u8{ 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
    var start: usize = 2; // var to make it runtime-known
    _ = &start; // suppress 'var is never mutated' error
    const slice = array[start..4];
    try expect(slice.len == 2);

    try expect(array[3] == 4);
    slice[1] += 1;
    try expect(array[3] == 5);
}

$ zig test test_slice_bounds.zig
1/1 test_slice_bounds.test.pointer slicing...OK
All 1 tests passed.

const expect = @import("std").testing.expect;

test "comptime pointers" {
    comptime {
        var x: i32 = 1;
        const ptr = &x;
        ptr.* += 1;
        x += 1;
        try expect(ptr.* == 3);
    }
}

$ zig test test_comptime_pointers.zig
1/1 test_comptime_pointers.test.comptime pointers...OK
All 1 tests passed.

const expect = @import("std").testing.expect;

test "@intFromPtr and @ptrFromInt" {
    const ptr: *i32 = @ptrFromInt(0xdeadbee0);
    const addr = @intFromPtr(ptr);
    try expect(@TypeOf(addr) == usize);
    try expect(addr == 0xdeadbee0);
}

$ zig test test_integer_pointer_conversion.zig
1/1 test_integer_pointer_conversion.test.@intFromPtr and @ptrFromInt...OK
All 1 tests passed.

const expect = @import("std").testing.expect;

test "comptime @ptrFromInt" {
    comptime {
        // Zig is able to do this at compile-time, as long as
        // ptr is never dereferenced.
        const ptr: *i32 = @ptrFromInt(0xdeadbee0);
        const addr = @intFromPtr(ptr);
        try expect(@TypeOf(addr) == usize);
        try expect(addr == 0xdeadbee0);
    }
}

$ zig test test_comptime_pointer_conversion.zig
1/1 test_comptime_pointer_conversion.test.comptime @ptrFromInt...OK
All 1 tests passed.

const expect = @import("std").testing.expect;

test "volatile" {
    const mmio_ptr: *volatile u8 = @ptrFromInt(0x12345678);
    try expect(@TypeOf(mmio_ptr) == *volatile u8);
}

$ zig test test_volatile.zig
1/1 test_volatile.test.volatile...OK
All 1 tests passed.

const std = @import("std");
const expect = std.testing.expect;

test "pointer casting" {
    const bytes align(@alignOf(u32)) = [_]u8{ 0x12, 0x12, 0x12, 0x12 };
    const u32_ptr: *const u32 = @ptrCast(&bytes);
    try expect(u32_ptr.* == 0x12121212);

    // Even this example is contrived - there are better ways to do the above than
    // pointer casting. For example, using a slice narrowing cast:
    const u32_value = std.mem.bytesAsSlice(u32, bytes[0..])[0];
    try expect(u32_value == 0x12121212);

    // And even another way, the most straightforward way to do it:
    try expect(@as(u32, @bitCast(bytes)) == 0x12121212);
}

test "pointer child type" {
    // pointer types have a `child` field which tells you the type they point to.
    try expect(@typeInfo(*u32).Pointer.child == u32);
}

$ zig test test_pointer_casting.zig
1/2 test_pointer_casting.test.pointer casting...OK
2/2 test_pointer_casting.test.pointer child type...OK
All 2 tests passed.

const std = @import("std");
const builtin = @import("builtin");
const expect = std.testing.expect;

test "variable alignment" {
    var x: i32 = 1234;
    const align_of_i32 = @alignOf(@TypeOf(x));
    try expect(@TypeOf(&x) == *i32);
    try expect(*i32 == *align(align_of_i32) i32);
    if (builtin.target.cpu.arch == .x86_64) {
        try expect(@typeInfo(*i32).Pointer.alignment == 4);
    }
}

$ zig test test_variable_alignment.zig
1/1 test_variable_alignment.test.variable alignment...OK
All 1 tests passed.

const expect = @import("std").testing.expect;

var foo: u8 align(4) = 100;

test "global variable alignment" {
    try expect(@typeInfo(@TypeOf(&foo)).Pointer.alignment == 4);
    try expect(@TypeOf(&foo) == *align(4) u8);
    const as_pointer_to_array: *align(4) [1]u8 = &foo;
    const as_slice: []align(4) u8 = as_pointer_to_array;
    const as_unaligned_slice: []u8 = as_slice;
    try expect(as_unaligned_slice[0] == 100);
}

fn derp() align(@sizeOf(usize) * 2) i32 {
    return 1234;
}
fn noop1() align(1) void {}
fn noop4() align(4) void {}

test "function alignment" {
    try expect(derp() == 1234);
    try expect(@TypeOf(derp) == fn () i32);
    try expect(@TypeOf(&derp) == *align(@sizeOf(usize) * 2) const fn () i32);

    noop1();
    try expect(@TypeOf(noop1) == fn () void);
    try expect(@TypeOf(&noop1) == *align(1) const fn () void);

    noop4();
    try expect(@TypeOf(noop4) == fn () void);
    try expect(@TypeOf(&noop4) == *align(4) const fn () void);
}

$ zig test test_variable_func_alignment.zig
1/2 test_variable_func_alignment.test.global variable alignment...OK
2/2 test_variable_func_alignment.test.function alignment...OK
All 2 tests passed.

const std = @import("std");

test "pointer alignment safety" {
    var array align(4) = [_]u32{ 0x11111111, 0x11111111 };
    const bytes = std.mem.sliceAsBytes(array[0..]);
    try std.testing.expect(foo(bytes) == 0x11111111);
}
fn foo(bytes: []u8) u32 {
    const slice4 = bytes[1..5];
    const int_slice = std.mem.bytesAsSlice(u32, @as([]align(4) u8, @alignCast(slice4)));
    return int_slice[0];
}

$ zig test test_incorrect_pointer_alignment.zig
1/1 test_incorrect_pointer_alignment.test.pointer alignment safety...thread 3568823 panic: incorrect alignment
/home/andy/src/zig/doc/langref/test_incorrect_pointer_alignment.zig:10:68: 0x103d13a in foo (test)
    const int_slice = std.mem.bytesAsSlice(u32, @as([]align(4) u8, @alignCast(slice4)));
                                                                   ^
/home/andy/src/zig/doc/langref/test_incorrect_pointer_alignment.zig:6:31: 0x103cfd7 in test.pointer alignment safety (test)
    try std.testing.expect(foo(bytes) == 0x11111111);
                              ^
/home/andy/src/zig/lib/compiler/test_runner.zig:157:25: 0x1047f10 in mainTerminal (test)
        if (test_fn.func()) |_| {
                        ^
/home/andy/src/zig/lib/compiler/test_runner.zig:37:28: 0x103e28b in main (test)
        return mainTerminal();
                           ^
/home/andy/src/zig/lib/std/start.zig:514:22: 0x103d609 in posixCallMainAndExit (test)
            root.main();
                     ^
/home/andy/src/zig/lib/std/start.zig:266:5: 0x103d171 in _start (test)
    asm volatile (switch (native_arch) {
    ^
???:?:?: 0x0 in ??? (???)
error: the following test command crashed:
/home/andy/src/zig/.zig-cache/o/c771705677c0d2df24e00269a9189f97/test

const std = @import("std");
const expect = std.testing.expect;

test "allowzero" {
    var zero: usize = 0; // var to make to runtime-known
    _ = &zero; // suppress 'var is never mutated' error
    const ptr: *allowzero i32 = @ptrFromInt(zero);
    try expect(@intFromPtr(ptr) == 0);
}

$ zig test test_allowzero.zig
1/1 test_allowzero.test.allowzero...OK
All 1 tests passed.

const std = @import("std");

// This is also available as `std.c.printf`.
pub extern "c" fn printf(format: [*:0]const u8, ...) c_int;

pub fn main() anyerror!void {
    _ = printf("Hello, world!\n"); // OK

    const msg = "Hello, world!\n";
    const non_null_terminated_msg: [msg.len]u8 = msg.*;
    _ = printf(&non_null_terminated_msg);
}

$ zig build-exe sentinel-terminated_pointer.zig -lc
/home/andy/src/zig/doc/langref/sentinel-terminated_pointer.zig:11:16: error: expected type '[*:0]const u8', found '*const [14]u8'
    _ = printf(&non_null_terminated_msg);
               ^~~~~~~~~~~~~~~~~~~~~~~~
/home/andy/src/zig/doc/langref/sentinel-terminated_pointer.zig:11:16: note: destination pointer requires '0' sentinel
/home/andy/src/zig/doc/langref/sentinel-terminated_pointer.zig:4:35: note: parameter type declared here
pub extern "c" fn printf(format: [*:0]const u8, ...) c_int;
                                 ~^~~~~~~~~~~~
referenced by:
    callMain: /home/andy/src/zig/lib/std/start.zig:524:32
    callMainWithArgs: /home/andy/src/zig/lib/std/start.zig:482:12
    remaining reference traces hidden; use '-freference-trace' to see all reference traces

const expect = @import("std").testing.expect;
const expectEqualSlices = @import("std").testing.expectEqualSlices;

test "basic slices" {
    var array = [_]i32{ 1, 2, 3, 4 };
    var known_at_runtime_zero: usize = 0;
    _ = &known_at_runtime_zero;
    const slice = array[known_at_runtime_zero..array.len];

    // alternative initialization using result location
    const alt_slice: []const i32 = &.{ 1, 2, 3, 4 };

    try expectEqualSlices(i32, slice, alt_slice);

    try expect(@TypeOf(slice) == []i32);
    try expect(&slice[0] == &array[0]);
    try expect(slice.len == array.len);

    // If you slice with comptime-known start and end positions, the result is
    // a pointer to an array, rather than a slice.
    const array_ptr = array[0..array.len];
    try expect(@TypeOf(array_ptr) == *[array.len]i32);

    // You can perform a slice-by-length by slicing twice. This allows the compiler
    // to perform some optimisations like recognising a comptime-known length when
    // the start position is only known at runtime.
    var runtime_start: usize = 1;
    _ = &runtime_start;
    const length = 2;
    const array_ptr_len = array[runtime_start..][0..length];
    try expect(@TypeOf(array_ptr_len) == *[length]i32);

    // Using the address-of operator on a slice gives a single-item pointer.
    try expect(@TypeOf(&slice[0]) == *i32);
    // Using the `ptr` field gives a many-item pointer.
    try expect(@TypeOf(slice.ptr) == [*]i32);
    try expect(@intFromPtr(slice.ptr) == @intFromPtr(&slice[0]));

    // Slices have array bounds checking. If you try to access something out
    // of bounds, you'll get a safety check failure:
    slice[10] += 1;

    // Note that `slice.ptr` does not invoke safety checking, while `&slice[0]`
    // asserts that the slice has len > 0.
}

$ zig test test_basic_slices.zig
1/1 test_basic_slices.test.basic slices...thread 3571722 panic: index out of bounds: index 10, len 4
/home/andy/src/zig/doc/langref/test_basic_slices.zig:41:10: 0x103f955 in test.basic slices (test)
    slice[10] += 1;
         ^
/home/andy/src/zig/lib/compiler/test_runner.zig:157:25: 0x104c800 in mainTerminal (test)
        if (test_fn.func()) |_| {
                        ^
/home/andy/src/zig/lib/compiler/test_runner.zig:37:28: 0x104210b in main (test)
        return mainTerminal();
                           ^
/home/andy/src/zig/lib/std/start.zig:514:22: 0x103fe49 in posixCallMainAndExit (test)
            root.main();
                     ^
/home/andy/src/zig/lib/std/start.zig:266:5: 0x103f9b1 in _start (test)
    asm volatile (switch (native_arch) {
    ^
???:?:?: 0x0 in ??? (???)
error: the following test command crashed:
/home/andy/src/zig/.zig-cache/o/3c391d75c939ce98356b98dd812503b1/test

const std = @import("std");
const expect = std.testing.expect;
const mem = std.mem;
const fmt = std.fmt;

test "using slices for strings" {
    // Zig has no concept of strings. String literals are const pointers
    // to null-terminated arrays of u8, and by convention parameters
    // that are "strings" are expected to be UTF-8 encoded slices of u8.
    // Here we coerce *const [5:0]u8 and *const [6:0]u8 to []const u8
    const hello: []const u8 = "hello";
    const world: []const u8 = "世界";

    var all_together: [100]u8 = undefined;
    // You can use slice syntax with at least one runtime-known index on an
    // array to convert an array into a slice.
    var start: usize = 0;
    _ = &start;
    const all_together_slice = all_together[start..];
    // String concatenation example.
    const hello_world = try fmt.bufPrint(all_together_slice, "{s} {s}", .{ hello, world });

    // Generally, you can use UTF-8 and not worry about whether something is a
    // string. If you don't need to deal with individual characters, no need
    // to decode.
    try expect(mem.eql(u8, hello_world, "hello 世界"));
}

test "slice pointer" {
    var array: [10]u8 = undefined;
    const ptr = &array;
    try expect(@TypeOf(ptr) == *[10]u8);

    // A pointer to an array can be sliced just like an array:
    var start: usize = 0;
    var end: usize = 5;
    _ = .{ &start, &end };
    const slice = ptr[start..end];
    // The slice is mutable because we sliced a mutable pointer.
    try expect(@TypeOf(slice) == []u8);
    slice[2] = 3;
    try expect(array[2] == 3);

    // Again, slicing with comptime-known indexes will produce another pointer
    // to an array:
    const ptr2 = slice[2..3];
    try expect(ptr2.len == 1);
    try expect(ptr2[0] == 3);
    try expect(@TypeOf(ptr2) == *[1]u8);
}

$ zig test test_slices.zig
1/2 test_slices.test.using slices for strings...OK
2/2 test_slices.test.slice pointer...OK
All 2 tests passed.

const std = @import("std");
const expect = std.testing.expect;

test "0-terminated slice" {
    const slice: [:0]const u8 = "hello";

    try expect(slice.len == 5);
    try expect(slice[5] == 0);
}

$ zig test test_null_terminated_slice.zig
1/1 test_null_terminated_slice.test.0-terminated slice...OK
All 1 tests passed.

const std = @import("std");
const expect = std.testing.expect;

test "0-terminated slicing" {
    var array = [_]u8{ 3, 2, 1, 0, 3, 2, 1, 0 };
    var runtime_length: usize = 3;
    _ = &runtime_length;
    const slice = array[0..runtime_length :0];

    try expect(@TypeOf(slice) == [:0]u8);
    try expect(slice.len == 3);
}

$ zig test test_null_terminated_slicing.zig
1/1 test_null_terminated_slicing.test.0-terminated slicing...OK
All 1 tests passed.

const std = @import("std");
const expect = std.testing.expect;

test "sentinel mismatch" {
    var array = [_]u8{ 3, 2, 1, 0 };

    // Creating a sentinel-terminated slice from the array with a length of 2
    // will result in the value `1` occupying the sentinel element position.
    // This does not match the indicated sentinel value of `0` and will lead
    // to a runtime panic.
    var runtime_length: usize = 2;
    _ = &runtime_length;
    const slice = array[0..runtime_length :0];

    _ = slice;
}

$ zig test test_sentinel_mismatch.zig
1/1 test_sentinel_mismatch.test.sentinel mismatch...thread 3579807 panic: sentinel mismatch: expected 0, found 1
/home/andy/src/zig/doc/langref/test_sentinel_mismatch.zig:13:24: 0x103cf16 in test.sentinel mismatch (test)
    const slice = array[0..runtime_length :0];
                       ^
/home/andy/src/zig/lib/compiler/test_runner.zig:157:25: 0x1048aa0 in mainTerminal (test)
        if (test_fn.func()) |_| {
                        ^
/home/andy/src/zig/lib/compiler/test_runner.zig:37:28: 0x103eabb in main (test)
        return mainTerminal();
                           ^
/home/andy/src/zig/lib/std/start.zig:514:22: 0x103d4f9 in posixCallMainAndExit (test)
            root.main();
                     ^
/home/andy/src/zig/lib/std/start.zig:266:5: 0x103d061 in _start (test)
    asm volatile (switch (native_arch) {
    ^
???:?:?: 0x0 in ??? (???)
error: the following test command crashed:
/home/andy/src/zig/.zig-cache/o/2af8da0d34d396fbb50fa515cef10c72/test

// Declare a struct.
// Zig gives no guarantees about the order of fields and the size of
// the struct but the fields are guaranteed to be ABI-aligned.
const Point = struct {
    x: f32,
    y: f32,
};

// Maybe we want to pass it to OpenGL so we want to be particular about
// how the bytes are arranged.
const Point2 = packed struct {
    x: f32,
    y: f32,
};

// Declare an instance of a struct.
const p = Point{
    .x = 0.12,
    .y = 0.34,
};

// Maybe we're not ready to fill out some of the fields.
var p2 = Point{
    .x = 0.12,
    .y = undefined,
};

// Structs can have methods
// Struct methods are not special, they are only namespaced
// functions that you can call with dot syntax.
const Vec3 = struct {
    x: f32,
    y: f32,
    z: f32,

    pub fn init(x: f32, y: f32, z: f32) Vec3 {
        return Vec3{
            .x = x,
            .y = y,
            .z = z,
        };
    }

    pub fn dot(self: Vec3, other: Vec3) f32 {
        return self.x * other.x + self.y * other.y + self.z * other.z;
    }
};

const expect = @import("std").testing.expect;
test "dot product" {
    const v1 = Vec3.init(1.0, 0.0, 0.0);
    const v2 = Vec3.init(0.0, 1.0, 0.0);
    try expect(v1.dot(v2) == 0.0);

    // Other than being available to call with dot syntax, struct methods are
    // not special. You can reference them as any other declaration inside
    // the struct:
    try expect(Vec3.dot(v1, v2) == 0.0);
}

// Structs can have declarations.
// Structs can have 0 fields.
const Empty = struct {
    pub const PI = 3.14;
};
test "struct namespaced variable" {
    try expect(Empty.PI == 3.14);
    try expect(@sizeOf(Empty) == 0);

    // you can still instantiate an empty struct
    const does_nothing = Empty{};

    _ = does_nothing;
}

// struct field order is determined by the compiler for optimal performance.
// however, you can still calculate a struct base pointer given a field pointer:
fn setYBasedOnX(x: *f32, y: f32) void {
    const point: *Point = @fieldParentPtr("x", x);
    point.y = y;
}
test "field parent pointer" {
    var point = Point{
        .x = 0.1234,
        .y = 0.5678,
    };
    setYBasedOnX(&point.x, 0.9);
    try expect(point.y == 0.9);
}

// You can return a struct from a function. This is how we do generics
// in Zig:
fn LinkedList(comptime T: type) type {
    return struct {
        pub const Node = struct {
            prev: ?*Node,
            next: ?*Node,
            data: T,
        };

        first: ?*Node,
        last: ?*Node,
        len: usize,
    };
}

test "linked list" {
    // Functions called at compile-time are memoized. This means you can
    // do this:
    try expect(LinkedList(i32) == LinkedList(i32));

    const list = LinkedList(i32){
        .first = null,
        .last = null,
        .len = 0,
    };
    try expect(list.len == 0);

    // Since types are first class values you can instantiate the type
    // by assigning it to a variable:
    const ListOfInts = LinkedList(i32);
    try expect(ListOfInts == LinkedList(i32));

    var node = ListOfInts.Node{
        .prev = null,
        .next = null,
        .data = 1234,
    };
    const list2 = LinkedList(i32){
        .first = &node,
        .last = &node,
        .len = 1,
    };

    // When using a pointer to a struct, fields can be accessed directly,
    // without explicitly dereferencing the pointer.
    // So you can do
    try expect(list2.first.?.data == 1234);
    // instead of try expect(list2.first.?.*.data == 1234);
}

$ zig test test_structs.zig
1/4 test_structs.test.dot product...OK
2/4 test_structs.test.struct namespaced variable...OK
3/4 test_structs.test.field parent pointer...OK
4/4 test_structs.test.linked list...OK
All 4 tests passed.

const Foo = struct {
    a: i32 = 1234,
    b: i32,
};

test "default struct initialization fields" {
    const x: Foo = .{
        .b = 5,
    };
    if (x.a + x.b != 1239) {
        comptime unreachable;
    }
}

$ zig test struct_default_field_values.zig
1/1 struct_default_field_values.test.default struct initialization fields...OK
All 1 tests passed.

const Threshold = struct {
    minimum: f32 = 0.25,
    maximum: f32 = 0.75,

    const Category = enum { low, medium, high };

    fn categorize(t: Threshold, value: f32) Category {
        assert(t.maximum >= t.minimum);
        if (value < t.minimum) return .low;
        if (value > t.maximum) return .high;
        return .medium;
    }
};

pub fn main() !void {
    var threshold: Threshold = .{
        .maximum = 0.20,
    };
    const category = threshold.categorize(0.90);
    try std.io.getStdOut().writeAll(@tagName(category));
}

const std = @import("std");
const assert = std.debug.assert;

$ zig build-exe bad_default_value.zig
$ ./bad_default_value
thread 3570319 panic: reached unreachable code
/home/andy/src/zig/lib/std/debug.zig:412:14: 0x1037a6d in assert (bad_default_value)
    if (!ok) unreachable; // assertion failure
             ^
/home/andy/src/zig/doc/langref/bad_default_value.zig:8:15: 0x1034f59 in categorize (bad_default_value)
        assert(t.maximum >= t.minimum);
              ^
/home/andy/src/zig/doc/langref/bad_default_value.zig:19:42: 0x1034e8a in main (bad_default_value)
    const category = threshold.categorize(0.90);
                                         ^
/home/andy/src/zig/lib/std/start.zig:524:37: 0x1034da5 in posixCallMainAndExit (bad_default_value)
            const result = root.main() catch |err| {
                                    ^
/home/andy/src/zig/lib/std/start.zig:266:5: 0x10348c1 in _start (bad_default_value)
    asm volatile (switch (native_arch) {
    ^
???:?:?: 0x0 in ??? (???)
(process terminated by signal)

const Threshold = struct {
    minimum: f32,
    maximum: f32,

    const default: Threshold = .{
        .minimum = 0.25,
        .maximum = 0.75,
    };
};

const std = @import("std");
const native_endian = @import("builtin").target.cpu.arch.endian();
const expect = std.testing.expect;

const Full = packed struct {
    number: u16,
};
const Divided = packed struct {
    half1: u8,
    quarter3: u4,
    quarter4: u4,
};

test "@bitCast between packed structs" {
    try doTheTest();
    try comptime doTheTest();
}

fn doTheTest() !void {
    try expect(@sizeOf(Full) == 2);
    try expect(@sizeOf(Divided) == 2);
    const full = Full{ .number = 0x1234 };
    const divided: Divided = @bitCast(full);
    try expect(divided.half1 == 0x34);
    try expect(divided.quarter3 == 0x2);
    try expect(divided.quarter4 == 0x1);

    const ordered: [2]u8 = @bitCast(full);
    switch (native_endian) {
        .big => {
            try expect(ordered[0] == 0x12);
            try expect(ordered[1] == 0x34);
        },
        .little => {
            try expect(ordered[0] == 0x34);
            try expect(ordered[1] == 0x12);
        },
    }
}

$ zig test test_packed_structs.zig
1/1 test_packed_structs.test.@bitCast between packed structs...OK
All 1 tests passed.

test "missized packed struct" {
    const S = packed struct(u32) { a: u16, b: u8 };
    _ = S{ .a = 4, .b = 2 };
}

$ zig test test_missized_packed_struct.zig
doc/langref/test_missized_packed_struct.zig:2:29: error: backing integer type 'u32' has bit size 32 but the struct fields have a total bit size of 24
    const S = packed struct(u32) { a: u16, b: u8 };
                            ^~~

const std = @import("std");
const expect = std.testing.expect;

const BitField = packed struct {
    a: u3,
    b: u3,
    c: u2,
};

var foo = BitField{
    .a = 1,
    .b = 2,
    .c = 3,
};

test "pointer to non-byte-aligned field" {
    const ptr = &foo.b;
    try expect(ptr.* == 2);
}

$ zig test test_pointer_to_non-byte_aligned_field.zig
1/1 test_pointer_to_non-byte_aligned_field.test.pointer to non-byte-aligned field...OK
All 1 tests passed.

const std = @import("std");
const expect = std.testing.expect;

const BitField = packed struct {
    a: u3,
    b: u3,
    c: u2,
};

var bit_field = BitField{
    .a = 1,
    .b = 2,
    .c = 3,
};

test "pointer to non-byte-aligned field" {
    try expect(bar(&bit_field.b) == 2);
}

fn bar(x: *const u3) u3 {
    return x.*;
}

$ zig test test_misaligned_pointer.zig
doc/langref/test_misaligned_pointer.zig:17:20: error: expected type '*const u3', found '*align(1:3:1) u3'
    try expect(bar(&bit_field.b) == 2);
                   ^~~~~~~~~~~~
doc/langref/test_misaligned_pointer.zig:17:20: note: pointer host size '1' cannot cast into pointer host size '0'
doc/langref/test_misaligned_pointer.zig:17:20: note: pointer bit offset '3' cannot cast into pointer bit offset '0'
doc/langref/test_misaligned_pointer.zig:20:11: note: parameter type declared here
fn bar(x: *const u3) u3 {
          ^~~~~~~~~

const std = @import("std");
const expect = std.testing.expect;

const BitField = packed struct {
    a: u3,
    b: u3,
    c: u2,
};

var bit_field = BitField{
    .a = 1,
    .b = 2,
    .c = 3,
};

test "pointers of sub-byte-aligned fields share addresses" {
    try expect(@intFromPtr(&bit_field.a) == @intFromPtr(&bit_field.b));
    try expect(@intFromPtr(&bit_field.a) == @intFromPtr(&bit_field.c));
}

$ zig test test_packed_struct_field_address.zig
1/1 test_packed_struct_field_address.test.pointers of sub-byte-aligned fields share addresses...OK
All 1 tests passed.

const std = @import("std");
const expect = std.testing.expect;

const BitField = packed struct {
    a: u3,
    b: u3,
    c: u2,
};

test "offsets of non-byte-aligned fields" {
    comptime {
        try expect(@bitOffsetOf(BitField, "a") == 0);
        try expect(@bitOffsetOf(BitField, "b") == 3);
        try expect(@bitOffsetOf(BitField, "c") == 6);

        try expect(@offsetOf(BitField, "a") == 0);
        try expect(@offsetOf(BitField, "b") == 0);
        try expect(@offsetOf(BitField, "c") == 0);
    }
}

$ zig test test_bitOffsetOf_offsetOf.zig
1/1 test_bitOffsetOf_offsetOf.test.offsets of non-byte-aligned fields...OK
All 1 tests passed.

const std = @import("std");
const expect = std.testing.expect;

const S = packed struct {
    a: u32,
    b: u32,
};
test "overaligned pointer to packed struct" {
    var foo: S align(4) = .{ .a = 1, .b = 2 };
    const ptr: *align(4) S = &foo;
    const ptr_to_b: *u32 = &ptr.b;
    try expect(ptr_to_b.* == 2);
}

$ zig test test_overaligned_packed_struct.zig
1/1 test_overaligned_packed_struct.test.overaligned pointer to packed struct...OK
All 1 tests passed.

const std = @import("std");
const expectEqual = std.testing.expectEqual;

test "aligned struct fields" {
    const S = struct {
        a: u32 align(2),
        b: u32 align(64),
    };
    var foo = S{ .a = 1, .b = 2 };

    try expectEqual(64, @alignOf(S));
    try expectEqual(*align(2) u32, @TypeOf(&foo.a));
    try expectEqual(*align(64) u32, @TypeOf(&foo.b));
}

$ zig test test_aligned_struct_fields.zig
1/1 test_aligned_struct_fields.test.aligned struct fields...OK
All 1 tests passed.

const std = @import("std");

pub fn main() void {
    const Foo = struct {};
    std.debug.print("variable: {s}\n", .{@typeName(Foo)});
    std.debug.print("anonymous: {s}\n", .{@typeName(struct {})});
    std.debug.print("function: {s}\n", .{@typeName(List(i32))});
}

fn List(comptime T: type) type {
    return struct {
        x: T,
    };
}

$ zig build-exe struct_name.zig
$ ./struct_name
variable: struct_name.main.Foo
anonymous: struct_name.main__struct_3331
function: struct_name.List(i32)

const std = @import("std");
const expect = std.testing.expect;

const Point = struct { x: i32, y: i32 };

test "anonymous struct literal" {
    const pt: Point = .{
        .x = 13,
        .y = 67,
    };
    try expect(pt.x == 13);
    try expect(pt.y == 67);
}

$ zig test test_struct_result.zig
1/1 test_struct_result.test.anonymous struct literal...OK
All 1 tests passed.

const std = @import("std");
const expect = std.testing.expect;

test "fully anonymous struct" {
    try check(.{
        .int = @as(u32, 1234),
        .float = @as(f64, 12.34),
        .b = true,
        .s = "hi",
    });
}

fn check(args: anytype) !void {
    try expect(args.int == 1234);
    try expect(args.float == 12.34);
    try expect(args.b);
    try expect(args.s[0] == 'h');
    try expect(args.s[1] == 'i');
}

$ zig test test_anonymous_struct.zig
1/1 test_anonymous_struct.test.fully anonymous struct...OK
All 1 tests passed.

const std = @import("std");
const expect = std.testing.expect;

test "tuple" {
    const values = .{
        @as(u32, 1234),
        @as(f64, 12.34),
        true,
        "hi",
    } ++ .{false} ** 2;
    try expect(values[0] == 1234);
    try expect(values[4] == false);
    inline for (values, 0..) |v, i| {
        if (i != 2) continue;
        try expect(v);
    }
    try expect(values.len == 6);
    try expect(values.@"3"[0] == 'h');
}

$ zig test test_tuples.zig
1/1 test_tuples.test.tuple...OK
All 1 tests passed.

const expect = @import("std").testing.expect;
const mem = @import("std").mem;

// Declare an enum.
const Type = enum {
    ok,
    not_ok,
};

// Declare a specific enum field.
const c = Type.ok;

// If you want access to the ordinal value of an enum, you
// can specify the tag type.
const Value = enum(u2) {
    zero,
    one,
    two,
};
// Now you can cast between u2 and Value.
// The ordinal value starts from 0, counting up by 1 from the previous member.
test "enum ordinal value" {
    try expect(@intFromEnum(Value.zero) == 0);
    try expect(@intFromEnum(Value.one) == 1);
    try expect(@intFromEnum(Value.two) == 2);
}

// You can override the ordinal value for an enum.
const Value2 = enum(u32) {
    hundred = 100,
    thousand = 1000,
    million = 1000000,
};
test "set enum ordinal value" {
    try expect(@intFromEnum(Value2.hundred) == 100);
    try expect(@intFromEnum(Value2.thousand) == 1000);
    try expect(@intFromEnum(Value2.million) == 1000000);
}

// You can also override only some values.
const Value3 = enum(u4) {
    a,
    b = 8,
    c,
    d = 4,
    e,
};
test "enum implicit ordinal values and overridden values" {
    try expect(@intFromEnum(Value3.a) == 0);
    try expect(@intFromEnum(Value3.b) == 8);
    try expect(@intFromEnum(Value3.c) == 9);
    try expect(@intFromEnum(Value3.d) == 4);
    try expect(@intFromEnum(Value3.e) == 5);
}

// Enums can have methods, the same as structs and unions.
// Enum methods are not special, they are only namespaced
// functions that you can call with dot syntax.
const Suit = enum {
    clubs,
    spades,
    diamonds,
    hearts,

    pub fn isClubs(self: Suit) bool {
        return self == Suit.clubs;
    }
};
test "enum method" {
    const p = Suit.spades;
    try expect(!p.isClubs());
}

// An enum can be switched upon.
const Foo = enum {
    string,
    number,
    none,
};
test "enum switch" {
    const p = Foo.number;
    const what_is_it = switch (p) {
        Foo.string => "this is a string",
        Foo.number => "this is a number",
        Foo.none => "this is a none",
    };
    try expect(mem.eql(u8, what_is_it, "this is a number"));
}

// @typeInfo can be used to access the integer tag type of an enum.
const Small = enum {
    one,
    two,
    three,
    four,
};
test "std.meta.Tag" {
    try expect(@typeInfo(Small).Enum.tag_type == u2);
}

// @typeInfo tells us the field count and the fields names:
test "@typeInfo" {
    try expect(@typeInfo(Small).Enum.fields.len == 4);
    try expect(mem.eql(u8, @typeInfo(Small).Enum.fields[1].name, "two"));
}

// @tagName gives a [:0]const u8 representation of an enum value:
test "@tagName" {
    try expect(mem.eql(u8, @tagName(Small.three), "three"));
}

$ zig test test_enums.zig
1/8 test_enums.test.enum ordinal value...OK
2/8 test_enums.test.set enum ordinal value...OK
3/8 test_enums.test.enum implicit ordinal values and overridden values...OK
4/8 test_enums.test.enum method...OK
5/8 test_enums.test.enum switch...OK
6/8 test_enums.test.std.meta.Tag...OK
7/8 test_enums.test.@typeInfo...OK
8/8 test_enums.test.@tagName...OK
All 8 tests passed.

const Foo = enum { a, b, c };
export fn entry(foo: Foo) void {
    _ = foo;
}

$ zig build-obj enum_export_error.zig
doc/langref/enum_export_error.zig:2:17: error: parameter of type 'enum_export_error.Foo' not allowed in function with calling convention 'C'
export fn entry(foo: Foo) void {
                ^~~~~~~~
doc/langref/enum_export_error.zig:2:17: note: enum tag type 'u2' is not extern compatible
doc/langref/enum_export_error.zig:2:17: note: only integers with 0, 8, 16, 32, 64 and 128 bits are extern compatible
doc/langref/enum_export_error.zig:1:13: note: enum declared here
const Foo = enum { a, b, c };
            ^~~~~~~~~~~~~~~~

const Foo = enum(c_int) { a, b, c };
export fn entry(foo: Foo) void {
    _ = foo;
}

$ zig build-obj enum_export.zig

const std = @import("std");
const expect = std.testing.expect;

const Color = enum {
    auto,
    off,
    on,
};

test "enum literals" {
    const color1: Color = .auto;
    const color2 = Color.auto;
    try expect(color1 == color2);
}

test "switch using enum literals" {
    const color = Color.on;
    const result = switch (color) {
        .auto => false,
        .on => true,
        .off => false,
    };
    try expect(result);
}

$ zig test test_enum_literals.zig
1/2 test_enum_literals.test.enum literals...OK
2/2 test_enum_literals.test.switch using enum literals...OK
All 2 tests passed.

const std = @import("std");
const expect = std.testing.expect;

const Number = enum(u8) {
    one,
    two,
    three,
    _,
};

test "switch on non-exhaustive enum" {
    const number = Number.one;
    const result = switch (number) {
        .one => true,
        .two, .three => false,
        _ => false,
    };
    try expect(result);
    const is_one = switch (number) {
        .one => true,
        else => false,
    };
    try expect(is_one);
}

$ zig test test_switch_non-exhaustive.zig
1/1 test_switch_non-exhaustive.test.switch on non-exhaustive enum...OK
All 1 tests passed.

const Payload = union {
    int: i64,
    float: f64,
    boolean: bool,
};
test "simple union" {
    var payload = Payload{ .int = 1234 };
    payload.float = 12.34;
}

$ zig test test_wrong_union_access.zig
1/1 test_wrong_union_access.test.simple union...thread 3579408 panic: access of union field 'float' while field 'int' is active
/home/andy/src/zig/doc/langref/test_wrong_union_access.zig:8:12: 0x103ce87 in test.simple union (test)
    payload.float = 12.34;
           ^
/home/andy/src/zig/lib/compiler/test_runner.zig:157:25: 0x1048070 in mainTerminal (test)
        if (test_fn.func()) |_| {
                        ^
/home/andy/src/zig/lib/compiler/test_runner.zig:37:28: 0x103e08b in main (test)
        return mainTerminal();
                           ^
/home/andy/src/zig/lib/std/start.zig:514:22: 0x103d419 in posixCallMainAndExit (test)
            root.main();
                     ^
/home/andy/src/zig/lib/std/start.zig:266:5: 0x103cf81 in _start (test)
    asm volatile (switch (native_arch) {
    ^
???:?:?: 0x0 in ??? (???)
error: the following test command crashed:
/home/andy/src/zig/.zig-cache/o/bb9968225995fac0bbc9f2116e8583c2/test

const std = @import("std");
const expect = std.testing.expect;

const Payload = union {
    int: i64,
    float: f64,
    boolean: bool,
};
test "simple union" {
    var payload = Payload{ .int = 1234 };
    try expect(payload.int == 1234);
    payload = Payload{ .float = 12.34 };
    try expect(payload.float == 12.34);
}

$ zig test test_simple_union.zig
1/1 test_simple_union.test.simple union...OK
All 1 tests passed.

const std = @import("std");
const expect = std.testing.expect;

const ComplexTypeTag = enum {
    ok,
    not_ok,
};
const ComplexType = union(ComplexTypeTag) {
    ok: u8,
    not_ok: void,
};

test "switch on tagged union" {
    const c = ComplexType{ .ok = 42 };
    try expect(@as(ComplexTypeTag, c) == ComplexTypeTag.ok);

    switch (c) {
        ComplexTypeTag.ok => |value| try expect(value == 42),
        ComplexTypeTag.not_ok => unreachable,
    }
}

test "get tag type" {
    try expect(std.meta.Tag(ComplexType) == ComplexTypeTag);
}

$ zig test test_tagged_union.zig
1/2 test_tagged_union.test.switch on tagged union...OK
2/2 test_tagged_union.test.get tag type...OK
All 2 tests passed.

const std = @import("std");
const expect = std.testing.expect;

const ComplexTypeTag = enum {
    ok,
    not_ok,
};
const ComplexType = union(ComplexTypeTag) {
    ok: u8,
    not_ok: void,
};

test "modify tagged union in switch" {
    var c = ComplexType{ .ok = 42 };

    switch (c) {
        ComplexTypeTag.ok => |*value| value.* += 1,
        ComplexTypeTag.not_ok => unreachable,
    }

    try expect(c.ok == 43);
}

$ zig test test_switch_modify_tagged_union.zig
1/1 test_switch_modify_tagged_union.test.modify tagged union in switch...OK
All 1 tests passed.

const std = @import("std");
const expect = std.testing.expect;

const Variant = union(enum) {
    int: i32,
    boolean: bool,

    // void can be omitted when inferring enum tag type.
    none,

    fn truthy(self: Variant) bool {
        return switch (self) {
            Variant.int => |x_int| x_int != 0,
            Variant.boolean => |x_bool| x_bool,
            Variant.none => false,
        };
    }
};

test "union method" {
    var v1 = Variant{ .int = 1 };
    var v2 = Variant{ .boolean = false };

    try expect(v1.truthy());
    try expect(!v2.truthy());
}

$ zig test test_union_method.zig
1/1 test_union_method.test.union method...OK
All 1 tests passed.

const std = @import("std");
const expect = std.testing.expect;

const Small2 = union(enum) {
    a: i32,
    b: bool,
    c: u8,
};
test "@tagName" {
    try expect(std.mem.eql(u8, @tagName(Small2.a), "a"));
}

$ zig test test_tagName.zig
1/1 test_tagName.test.@tagName...OK
All 1 tests passed.

const std = @import("std");
const expect = std.testing.expect;

const Number = union {
    int: i32,
    float: f64,
};

test "anonymous union literal syntax" {
    const i: Number = .{ .int = 42 };
    const f = makeNumber();
    try expect(i.int == 42);
    try expect(f.float == 12.34);
}

fn makeNumber() Number {
    return .{ .float = 12.34 };
}

$ zig test test_anonymous_union.zig
1/1 test_anonymous_union.test.anonymous union literal syntax...OK
All 1 tests passed.

const Derp = opaque {};
const Wat = opaque {};

extern fn bar(d: *Derp) void;
fn foo(w: *Wat) callconv(.C) void {
    bar(w);
}

test "call foo" {
    foo(undefined);
}

$ zig test test_opaque.zig
doc/langref/test_opaque.zig:6:9: error: expected type '*test_opaque.Derp', found '*test_opaque.Wat'
    bar(w);
        ^
doc/langref/test_opaque.zig:6:9: note: pointer type child 'test_opaque.Wat' cannot cast into pointer type child 'test_opaque.Derp'
doc/langref/test_opaque.zig:2:13: note: opaque declared here
const Wat = opaque {};
            ^~~~~~~~~
doc/langref/test_opaque.zig:1:14: note: opaque declared here
const Derp = opaque {};
             ^~~~~~~~~
doc/langref/test_opaque.zig:4:18: note: parameter type declared here
extern fn bar(d: *Derp) void;
                 ^~~~~
referenced by:
    test.call foo: doc/langref/test_opaque.zig:10:5
    remaining reference traces hidden; use '-freference-trace' to see all reference traces

test "access variable after block scope" {
    {
        var x: i32 = 1;
        _ = &x;
    }
    x += 1;
}

$ zig test test_blocks.zig
doc/langref/test_blocks.zig:6:5: error: use of undeclared identifier 'x'
    x += 1;
    ^

const std = @import("std");
const expect = std.testing.expect;

test "labeled break from labeled block expression" {
    var y: i32 = 123;

    const x = blk: {
        y += 1;
        break :blk y;
    };
    try expect(x == 124);
    try expect(y == 124);
}

$ zig test test_labeled_break.zig
1/1 test_labeled_break.test.labeled break from labeled block expression...OK
All 1 tests passed.

const pi = 3.14;

test "inside test block" {
    // Let's even go inside another block
    {
        var pi: i32 = 1234;
    }
}

$ zig test test_shadowing.zig
doc/langref/test_shadowing.zig:6:13: error: local variable shadows declaration of 'pi'
        var pi: i32 = 1234;
            ^~
doc/langref/test_shadowing.zig:1:1: note: declared here
const pi = 3.14;
^~~~~~~~~~~~~~~

test "separate scopes" {
    {
        const pi = 3.14;
        _ = pi;
    }
    {
        var pi: bool = true;
        _ = π
    }
}

$ zig test test_scopes.zig
1/1 test_scopes.test.separate scopes...OK
All 1 tests passed.

const std = @import("std");
const expect = std.testing.expect;

test {
    const a = {};
    const b = void{};
    try expect(@TypeOf(a) == void);
    try expect(@TypeOf(b) == void);
    try expect(a == b);
}

$ zig test test_empty_block.zig
1/1 test_empty_block.test_0...OK
All 1 tests passed.

const std = @import("std");
const builtin = @import("builtin");
const expect = std.testing.expect;

test "switch simple" {
    const a: u64 = 10;
    const zz: u64 = 103;

    // All branches of a switch expression must be able to be coerced to a
    // common type.
    //
    // Branches cannot fallthrough. If fallthrough behavior is desired, combine
    // the cases and use an if.
    const b = switch (a) {
        // Multiple cases can be combined via a ','
        1, 2, 3 => 0,

        // Ranges can be specified using the ... syntax. These are inclusive
        // of both ends.
        5...100 => 1,

        // Branches can be arbitrarily complex.
        101 => blk: {
            const c: u64 = 5;
            break :blk c * 2 + 1;
        },

        // Switching on arbitrary expressions is allowed as long as the
        // expression is known at compile-time.
        zz => zz,
        blk: {
            const d: u32 = 5;
            const e: u32 = 100;
            break :blk d + e;
        } => 107,

        // The else branch catches everything not already captured.
        // Else branches are mandatory unless the entire range of values
        // is handled.
        else => 9,
    };

    try expect(b == 1);
}

// Switch expressions can be used outside a function:
const os_msg = switch (builtin.target.os.tag) {
    .linux => "we found a linux user",
    else => "not a linux user",
};

// Inside a function, switch statements implicitly are compile-time
// evaluated if the target expression is compile-time known.
test "switch inside function" {
    switch (builtin.target.os.tag) {
        .fuchsia => {
            // On an OS other than fuchsia, block is not even analyzed,
            // so this compile error is not triggered.
            // On fuchsia this compile error would be triggered.
            @compileError("fuchsia not supported");
        },
        else => {},
    }
}

$ zig test test_switch.zig
1/2 test_switch.test.switch simple...OK
2/2 test_switch.test.switch inside function...OK
All 2 tests passed.

const expect = @import("std").testing.expect;

test "switch on tagged union" {
    const Point = struct {
        x: u8,
        y: u8,
    };
    const Item = union(enum) {
        a: u32,
        c: Point,
        d,
        e: u32,
    };

    var a = Item{ .c = Point{ .x = 1, .y = 2 } };

    // Switching on more complex enums is allowed.
    const b = switch (a) {
        // A capture group is allowed on a match, and will return the enum
        // value matched. If the payload types of both cases are the same
        // they can be put into the same switch prong.
        Item.a, Item.e => |item| item,

        // A reference to the matched value can be obtained using `*` syntax.
        Item.c => |*item| blk: {
            item.*.x += 1;
            break :blk 6;
        },

        // No else is required if the types cases was exhaustively handled
        Item.d => 8,
    };

    try expect(b == 6);
    try expect(a.c.x == 2);
}

$ zig test test_switch_tagged_union.zig
1/1 test_switch_tagged_union.test.switch on tagged union...OK
All 1 tests passed.

const Color = enum {
    auto,
    off,
    on,
};

test "exhaustive switching" {
    const color = Color.off;
    switch (color) {
        Color.auto => {},
        Color.on => {},
    }
}

$ zig test test_unhandled_enumeration_value.zig
doc/langref/test_unhandled_enumeration_value.zig:9:5: error: switch must handle all possibilities
    switch (color) {
    ^~~~~~
doc/langref/test_unhandled_enumeration_value.zig:3:5: note: unhandled enumeration value: 'off'
    off,
    ^~~
doc/langref/test_unhandled_enumeration_value.zig:1:15: note: enum 'test_unhandled_enumeration_value.Color' declared here
const Color = enum {
              ^~~~

const std = @import("std");
const expect = std.testing.expect;

const Color = enum {
    auto,
    off,
    on,
};

test "enum literals with switch" {
    const color = Color.off;
    const result = switch (color) {
        .auto => false,
        .on => false,
        .off => true,
    };
    try expect(result);
}

$ zig test test_exhaustive_switch.zig
1/1 test_exhaustive_switch.test.enum literals with switch...OK
All 1 tests passed.

const std = @import("std");
const expect = std.testing.expect;
const expectError = std.testing.expectError;

fn isFieldOptional(comptime T: type, field_index: usize) !bool {
    const fields = @typeInfo(T).Struct.fields;
    return switch (field_index) {
        // This prong is analyzed twice with `idx` being a
        // comptime-known value each time.
        inline 0, 1 => |idx| @typeInfo(fields[idx].type) == .Optional,
        else => return error.IndexOutOfBounds,
    };
}

const Struct1 = struct { a: u32, b: ?u32 };

test "using @typeInfo with runtime values" {
    var index: usize = 0;
    try expect(!try isFieldOptional(Struct1, index));
    index += 1;
    try expect(try isFieldOptional(Struct1, index));
    index += 1;
    try expectError(error.IndexOutOfBounds, isFieldOptional(Struct1, index));
}

// Calls to `isFieldOptional` on `Struct1` get unrolled to an equivalent
// of this function:
fn isFieldOptionalUnrolled(field_index: usize) !bool {
    return switch (field_index) {
        0 => false,
        1 => true,
        else => return error.IndexOutOfBounds,
    };
}

$ zig test test_inline_switch.zig
1/1 test_inline_switch.test.using @typeInfo with runtime values...OK
All 1 tests passed.

fn isFieldOptional(comptime T: type, field_index: usize) !bool {
    const fields = @typeInfo(T).Struct.fields;
    return switch (field_index) {
        inline 0...fields.len - 1 => |idx| @typeInfo(fields[idx].type) == .Optional,
        else => return error.IndexOutOfBounds,
    };
}

const std = @import("std");
const expect = std.testing.expect;

const SliceTypeA = extern struct {
    len: usize,
    ptr: [*]u32,
};
const SliceTypeB = extern struct {
    ptr: [*]SliceTypeA,
    len: usize,
};
const AnySlice = union(enum) {
    a: SliceTypeA,
    b: SliceTypeB,
    c: []const u8,
    d: []AnySlice,
};

fn withFor(any: AnySlice) usize {
    const Tag = @typeInfo(AnySlice).Union.tag_type.?;
    inline for (@typeInfo(Tag).Enum.fields) |field| {
        // With `inline for` the function gets generated as
        // a series of `if` statements relying on the optimizer
        // to convert it to a switch.
        if (field.value == @intFromEnum(any)) {
            return @field(any, field.name).len;
        }
    }
    // When using `inline for` the compiler doesn't know that every
    // possible case has been handled requiring an explicit `unreachable`.
    unreachable;
}

fn withSwitch(any: AnySlice) usize {
    return switch (any) {
        // With `inline else` the function is explicitly generated
        // as the desired switch and the compiler can check that
        // every possible case is handled.
        inline else => |slice| slice.len,
    };
}

test "inline for and inline else similarity" {
    const any = AnySlice{ .c = "hello" };
    try expect(withFor(any) == 5);
    try expect(withSwitch(any) == 5);
}

$ zig test test_inline_else.zig
1/1 test_inline_else.test.inline for and inline else similarity...OK
All 1 tests passed.

const std = @import("std");
const expect = std.testing.expect;

const U = union(enum) {
    a: u32,
    b: f32,
};

fn getNum(u: U) u32 {
    switch (u) {
        // Here `num` is a runtime-known value that is either
        // `u.a` or `u.b` and `tag` is `u`'s comptime-known tag value.
        inline else => |num, tag| {
            if (tag == .b) {
                return @intFromFloat(num);
            }
            return num;
        },
    }
}

test "test" {
    const u = U{ .b = 42 };
    try expect(getNum(u) == 42);
}

$ zig test test_inline_switch_union_tag.zig
1/1 test_inline_switch_union_tag.test.test...OK
All 1 tests passed.

const expect = @import("std").testing.expect;

test "while basic" {
    var i: usize = 0;
    while (i < 10) {
        i += 1;
    }
    try expect(i == 10);
}

$ zig test test_while.zig
1/1 test_while.test.while basic...OK
All 1 tests passed.

const expect = @import("std").testing.expect;

test "while break" {
    var i: usize = 0;
    while (true) {
        if (i == 10)
            break;
        i += 1;
    }
    try expect(i == 10);
}

$ zig test test_while_break.zig
1/1 test_while_break.test.while break...OK
All 1 tests passed.

const expect = @import("std").testing.expect;

test "while continue" {
    var i: usize = 0;
    while (true) {
        i += 1;
        if (i < 10)
            continue;
        break;
    }
    try expect(i == 10);
}

$ zig test test_while_continue.zig
1/1 test_while_continue.test.while continue...OK
All 1 tests passed.

const expect = @import("std").testing.expect;

test "while loop continue expression" {
    var i: usize = 0;
    while (i < 10) : (i += 1) {}
    try expect(i == 10);
}

test "while loop continue expression, more complicated" {
    var i: usize = 1;
    var j: usize = 1;
    while (i * j < 2000) : ({
        i *= 2;
        j *= 3;
    }) {
        const my_ij = i * j;
        try expect(my_ij < 2000);
    }
}

$ zig test test_while_continue_expression.zig
1/2 test_while_continue_expression.test.while loop continue expression...OK
2/2 test_while_continue_expression.test.while loop continue expression, more complicated...OK
All 2 tests passed.

const expect = @import("std").testing.expect;

test "while else" {
    try expect(rangeHasNumber(0, 10, 5));
    try expect(!rangeHasNumber(0, 10, 15));
}

fn rangeHasNumber(begin: usize, end: usize, number: usize) bool {
    var i = begin;
    return while (i < end) : (i += 1) {
        if (i == number) {
            break true;
        }
    } else false;
}

$ zig test test_while_else.zig
1/1 test_while_else.test.while else...OK
All 1 tests passed.

test "nested break" {
    outer: while (true) {
        while (true) {
            break :outer;
        }
    }
}

test "nested continue" {
    var i: usize = 0;
    outer: while (i < 10) : (i += 1) {
        while (true) {
            continue :outer;
        }
    }
}

$ zig test test_while_nested_break.zig
1/2 test_while_nested_break.test.nested break...OK
2/2 test_while_nested_break.test.nested continue...OK
All 2 tests passed.

const expect = @import("std").testing.expect;

test "while null capture" {
    var sum1: u32 = 0;
    numbers_left = 3;
    while (eventuallyNullSequence()) |value| {
        sum1 += value;
    }
    try expect(sum1 == 3);

    // null capture with an else block
    var sum2: u32 = 0;
    numbers_left = 3;
    while (eventuallyNullSequence()) |value| {
        sum2 += value;
    } else {
        try expect(sum2 == 3);
    }

    // null capture with a continue expression
    var i: u32 = 0;
    var sum3: u32 = 0;
    numbers_left = 3;
    while (eventuallyNullSequence()) |value| : (i += 1) {
        sum3 += value;
    }
    try expect(i == 3);
}

var numbers_left: u32 = undefined;
fn eventuallyNullSequence() ?u32 {
    return if (numbers_left == 0) null else blk: {
        numbers_left -= 1;
        break :blk numbers_left;
    };
}

$ zig test test_while_null_capture.zig
1/1 test_while_null_capture.test.while null capture...OK
All 1 tests passed.

const expect = @import("std").testing.expect;

test "while error union capture" {
    var sum1: u32 = 0;
    numbers_left = 3;
    while (eventuallyErrorSequence()) |value| {
        sum1 += value;
    } else |err| {
        try expect(err == error.ReachedZero);
    }
}

var numbers_left: u32 = undefined;

fn eventuallyErrorSequence() anyerror!u32 {
    return if (numbers_left == 0) error.ReachedZero else blk: {
        numbers_left -= 1;
        break :blk numbers_left;
    };
}

$ zig test test_while_error_capture.zig
1/1 test_while_error_capture.test.while error union capture...OK
All 1 tests passed.

const expect = @import("std").testing.expect;

test "inline while loop" {
    comptime var i = 0;
    var sum: usize = 0;
    inline while (i < 3) : (i += 1) {
        const T = switch (i) {
            0 => f32,
            1 => i8,
            2 => bool,
            else => unreachable,
        };
        sum += typeNameLength(T);
    }
    try expect(sum == 9);
}

fn typeNameLength(comptime T: type) usize {
    return @typeName(T).len;
}

$ zig test test_inline_while.zig
1/1 test_inline_while.test.inline while loop...OK
All 1 tests passed.

const expect = @import("std").testing.expect;

test "for basics" {
    const items = [_]i32{ 4, 5, 3, 4, 0 };
    var sum: i32 = 0;

    // For loops iterate over slices and arrays.
    for (items) |value| {
        // Break and continue are supported.
        if (value == 0) {
            continue;
        }
        sum += value;
    }
    try expect(sum == 16);

    // To iterate over a portion of a slice, reslice.
    for (items[0..1]) |value| {
        sum += value;
    }
    try expect(sum == 20);

    // To access the index of iteration, specify a second condition as well
    // as a second capture value.
    var sum2: i32 = 0;
    for (items, 0..) |_, i| {
        try expect(@TypeOf(i) == usize);
        sum2 += @as(i32, @intCast(i));
    }
    try expect(sum2 == 10);

    // To iterate over consecutive integers, use the range syntax.
    // Unbounded range is always a compile error.
    var sum3: usize = 0;
    for (0..5) |i| {
        sum3 += i;
    }
    try expect(sum3 == 10);
}

test "multi object for" {
    const items = [_]usize{ 1, 2, 3 };
    const items2 = [_]usize{ 4, 5, 6 };
    var count: usize = 0;

    // Iterate over multiple objects.
    // All lengths must be equal at the start of the loop, otherwise detectable
    // illegal behavior occurs.
    for (items, items2) |i, j| {
        count += i + j;
    }

    try expect(count == 21);
}

test "for reference" {
    var items = [_]i32{ 3, 4, 2 };

    // Iterate over the slice by reference by
    // specifying that the capture value is a pointer.
    for (&items) |*value| {
        value.* += 1;
    }

    try expect(items[0] == 4);
    try expect(items[1] == 5);
    try expect(items[2] == 3);
}

test "for else" {
    // For allows an else attached to it, the same as a while loop.
    const items = [_]?i32{ 3, 4, null, 5 };

    // For loops can also be used as expressions.
    // Similar to while loops, when you break from a for loop, the else branch is not evaluated.
    var sum: i32 = 0;
    const result = for (items) |value| {
        if (value != null) {
            sum += value.?;
        }
    } else blk: {
        try expect(sum == 12);
        break :blk sum;
    };
    try expect(result == 12);
}

$ zig test test_for.zig
1/4 test_for.test.for basics...OK
2/4 test_for.test.multi object for...OK
3/4 test_for.test.for reference...OK
4/4 test_for.test.for else...OK
All 4 tests passed.

const std = @import("std");
const expect = std.testing.expect;

test "nested break" {
    var count: usize = 0;
    outer: for (1..6) |_| {
        for (1..6) |_| {
            count += 1;
            break :outer;
        }
    }
    try expect(count == 1);
}

test "nested continue" {
    var count: usize = 0;
    outer: for (1..9) |_| {
        for (1..6) |_| {
            count += 1;
            continue :outer;
        }
    }

    try expect(count == 8);
}

$ zig test test_for_nested_break.zig
1/2 test_for_nested_break.test.nested break...OK
2/2 test_for_nested_break.test.nested continue...OK
All 2 tests passed.

const expect = @import("std").testing.expect;

test "inline for loop" {
    const nums = [_]i32{ 2, 4, 6 };
    var sum: usize = 0;
    inline for (nums) |i| {
        const T = switch (i) {
            2 => f32,
            4 => i8,
            6 => bool,
            else => unreachable,
        };
        sum += typeNameLength(T);
    }
    try expect(sum == 9);
}

fn typeNameLength(comptime T: type) usize {
    return @typeName(T).len;
}

$ zig test test_inline_for.zig
1/1 test_inline_for.test.inline for loop...OK
All 1 tests passed.

// If expressions have three uses, corresponding to the three types:
// * bool
// * ?T
// * anyerror!T

const expect = @import("std").testing.expect;

test "if expression" {
    // If expressions are used instead of a ternary expression.
    const a: u32 = 5;
    const b: u32 = 4;
    const result = if (a != b) 47 else 3089;
    try expect(result == 47);
}

test "if boolean" {
    // If expressions test boolean conditions.
    const a: u32 = 5;
    const b: u32 = 4;
    if (a != b) {
        try expect(true);
    } else if (a == 9) {
        unreachable;
    } else {
        unreachable;
    }
}

test "if error union" {
    // If expressions test for errors.
    // Note the |err| capture on the else.

    const a: anyerror!u32 = 0;
    if (a) |value| {
        try expect(value == 0);
    } else |err| {
        _ = err;
        unreachable;
    }

    const b: anyerror!u32 = error.BadValue;
    if (b) |value| {
        _ = value;
        unreachable;
    } else |err| {
        try expect(err == error.BadValue);
    }

    // The else and |err| capture is strictly required.
    if (a) |value| {
        try expect(value == 0);
    } else |_| {}

    // To check only the error value, use an empty block expression.
    if (b) |_| {} else |err| {
        try expect(err == error.BadValue);
    }

    // Access the value by reference using a pointer capture.
    var c: anyerror!u32 = 3;
    if (c) |*value| {
        value.* = 9;
    } else |_| {
        unreachable;
    }

    if (c) |value| {
        try expect(value == 9);
    } else |_| {
        unreachable;
    }
}

$ zig test test_if.zig
1/3 test_if.test.if expression...OK
2/3 test_if.test.if boolean...OK
3/3 test_if.test.if error union...OK
All 3 tests passed.

const expect = @import("std").testing.expect;

test "if optional" {
    // If expressions test for null.

    const a: ?u32 = 0;
    if (a) |value| {
        try expect(value == 0);
    } else {
        unreachable;
    }

    const b: ?u32 = null;
    if (b) |_| {
        unreachable;
    } else {
        try expect(true);
    }

    // The else is not required.
    if (a) |value| {
        try expect(value == 0);
    }

    // To test against null only, use the binary equality operator.
    if (b == null) {
        try expect(true);
    }

    // Access the value by reference using a pointer capture.
    var c: ?u32 = 3;
    if (c) |*value| {
        value.* = 2;
    }

    if (c) |value| {
        try expect(value == 2);
    } else {
        unreachable;
    }
}

test "if error union with optional" {
    // If expressions test for errors before unwrapping optionals.
    // The |optional_value| capture's type is ?u32.

    const a: anyerror!?u32 = 0;
    if (a) |optional_value| {
        try expect(optional_value.? == 0);
    } else |err| {
        _ = err;
        unreachable;
    }

    const b: anyerror!?u32 = null;
    if (b) |optional_value| {
        try expect(optional_value == null);
    } else |_| {
        unreachable;
    }

    const c: anyerror!?u32 = error.BadValue;
    if (c) |optional_value| {
        _ = optional_value;
        unreachable;
    } else |err| {
        try expect(err == error.BadValue);
    }

    // Access the value by reference by using a pointer capture each time.
    var d: anyerror!?u32 = 3;
    if (d) |*optional_value| {
        if (optional_value.*) |*value| {
            value.* = 9;
        }
    } else |_| {
        unreachable;
    }

    if (d) |optional_value| {
        try expect(optional_value.? == 9);
    } else |_| {
        unreachable;
    }
}

$ zig test test_if_optionals.zig
1/2 test_if_optionals.test.if optional...OK
2/2 test_if_optionals.test.if error union with optional...OK
All 2 tests passed.

const std = @import("std");
const expect = std.testing.expect;
const print = std.debug.print;

fn deferExample() !usize {
    var a: usize = 1;

    {
        defer a = 2;
        a = 1;
    }
    try expect(a == 2);

    a = 5;
    return a;
}

test "defer basics" {
    try expect((try deferExample()) == 5);
}

$ zig test test_defer.zig
1/1 test_defer.test.defer basics...OK
All 1 tests passed.

const std = @import("std");
const expect = std.testing.expect;
const print = std.debug.print;

test "defer unwinding" {
    print("\n", .{});

    defer {
        print("1 ", .{});
    }
    defer {
        print("2 ", .{});
    }
    if (false) {
        // defers are not run if they are never executed.
        defer {
            print("3 ", .{});
        }
    }
}

$ zig test defer_unwind.zig
1/1 defer_unwind.test.defer unwinding...
2 1 OK
All 1 tests passed.

fn deferInvalidExample() !void {
    defer {
        return error.DeferError;
    }

    return error.DeferError;
}

$ zig test test_invalid_defer.zig
doc/langref/test_invalid_defer.zig:3:9: error: cannot return from defer expression
        return error.DeferError;
        ^~~~~~~~~~~~~~~~~~~~~~~
doc/langref/test_invalid_defer.zig:2:5: note: defer expression here
    defer {
    ^~~~~

// unreachable is used to assert that control flow will never reach a
// particular location:
test "basic math" {
    const x = 1;
    const y = 2;
    if (x + y != 3) {
        unreachable;
    }
}

$ zig test test_unreachable.zig
1/1 test_unreachable.test.basic math...OK
All 1 tests passed.

// This is how std.debug.assert is implemented
fn assert(ok: bool) void {
    if (!ok) unreachable; // assertion failure
}

// This test will fail because we hit unreachable.
test "this will fail" {
    assert(false);
}

$ zig test test_assertion_failure.zig
1/1 test_assertion_failure.test.this will fail...thread 3571599 panic: reached unreachable code
/home/andy/src/zig/doc/langref/test_assertion_failure.zig:3:14: 0x103cd9d in assert (test)
    if (!ok) unreachable; // assertion failure
             ^
/home/andy/src/zig/doc/langref/test_assertion_failure.zig:8:11: 0x103cd5a in test.this will fail (test)
    assert(false);
          ^
/home/andy/src/zig/lib/compiler/test_runner.zig:157:25: 0x10479a0 in mainTerminal (test)
        if (test_fn.func()) |_| {
                        ^
/home/andy/src/zig/lib/compiler/test_runner.zig:37:28: 0x103dbbb in main (test)
        return mainTerminal();
                           ^
/home/andy/src/zig/lib/std/start.zig:514:22: 0x103d249 in posixCallMainAndExit (test)
            root.main();
                     ^
/home/andy/src/zig/lib/std/start.zig:266:5: 0x103cdb1 in _start (test)
    asm volatile (switch (native_arch) {
    ^
???:?:?: 0x0 in ??? (???)
error: the following test command crashed:
/home/andy/src/zig/.zig-cache/o/a6b3ce5875a9e285c15739b2a1b30733/test

const assert = @import("std").debug.assert;

test "type of unreachable" {
    comptime {
        // The type of unreachable is noreturn.

        // However this assertion will still fail to compile because
        // unreachable expressions are compile errors.

        assert(@TypeOf(unreachable) == noreturn);
    }
}

$ zig test test_comptime_unreachable.zig
doc/langref/test_comptime_unreachable.zig:10:16: error: unreachable code
        assert(@TypeOf(unreachable) == noreturn);
               ^~~~~~~~~~~~~~~~~~~~
doc/langref/test_comptime_unreachable.zig:10:24: note: control flow is diverted here
        assert(@TypeOf(unreachable) == noreturn);
                       ^~~~~~~~~~~

fn foo(condition: bool, b: u32) void {
    const a = if (condition) b else return;
    _ = a;
    @panic("do something with a");
}
test "noreturn" {
    foo(false, 1);
}

$ zig test test_noreturn.zig
1/1 test_noreturn.test.noreturn...OK
All 1 tests passed.

const std = @import("std");
const builtin = @import("builtin");
const native_arch = builtin.cpu.arch;
const expect = std.testing.expect;

const WINAPI: std.builtin.CallingConvention = if (native_arch == .x86) .Stdcall else .C;
extern "kernel32" fn ExitProcess(exit_code: c_uint) callconv(WINAPI) noreturn;

test "foo" {
    const value = bar() catch ExitProcess(1);
    try expect(value == 1234);
}

fn bar() anyerror!u32 {
    return 1234;
}

$ zig test test_noreturn_from_exit.zig -target x86_64-windows --test-no-exec

const std = @import("std");
const builtin = @import("builtin");
const native_arch = builtin.cpu.arch;
const expect = std.testing.expect;

// Functions are declared like this
fn add(a: i8, b: i8) i8 {
    if (a == 0) {
        return b;
    }

    return a + b;
}

// The export specifier makes a function externally visible in the generated
// object file, and makes it use the C ABI.
export fn sub(a: i8, b: i8) i8 {
    return a - b;
}

// The extern specifier is used to declare a function that will be resolved
// at link time, when linking statically, or at runtime, when linking
// dynamically. The quoted identifier after the extern keyword specifies
// the library that has the function. (e.g. "c" -> libc.so)
// The callconv specifier changes the calling convention of the function.
const WINAPI: std.builtin.CallingConvention = if (native_arch == .x86) .Stdcall else .C;
extern "kernel32" fn ExitProcess(exit_code: u32) callconv(WINAPI) noreturn;
extern "c" fn atan2(a: f64, b: f64) f64;

// The @setCold builtin tells the optimizer that a function is rarely called.
fn abort() noreturn {
    @setCold(true);
    while (true) {}
}

// The naked calling convention makes a function not have any function prologue or epilogue.
// This can be useful when integrating with assembly.
fn _start() callconv(.Naked) noreturn {
    abort();
}

// The inline calling convention forces a function to be inlined at all call sites.
// If the function cannot be inlined, it is a compile-time error.
inline fn shiftLeftOne(a: u32) u32 {
    return a << 1;
}

// The pub specifier allows the function to be visible when importing.
// Another file can use @import and call sub2
pub fn sub2(a: i8, b: i8) i8 {
    return a - b;
}

// Function pointers are prefixed with `*const `.
const Call2Op = *const fn (a: i8, b: i8) i8;
fn doOp(fnCall: Call2Op, op1: i8, op2: i8) i8 {
    return fnCall(op1, op2);
}

test "function" {
    try expect(doOp(add, 5, 6) == 11);
    try expect(doOp(sub2, 5, 6) == -1);
}

$ zig test test_functions.zig
1/1 test_functions.test.function...OK
All 1 tests passed.

const Point = struct {
    x: i32,
    y: i32,
};

fn foo(point: Point) i32 {
    // Here, `point` could be a reference, or a copy. The function body
    // can ignore the difference and treat it as a value. Be very careful
    // taking the address of the parameter - it should be treated as if
    // the address will become invalid when the function returns.
    return point.x + point.y;
}

const expect = @import("std").testing.expect;

test "pass struct to function" {
    try expect(foo(Point{ .x = 1, .y = 2 }) == 3);
}

$ zig test test_pass_by_reference_or_value.zig
1/1 test_pass_by_reference_or_value.test.pass struct to function...OK
All 1 tests passed.

const expect = @import("std").testing.expect;

fn addFortyTwo(x: anytype) @TypeOf(x) {
    return x + 42;
}

test "fn type inference" {
    try expect(addFortyTwo(1) == 43);
    try expect(@TypeOf(addFortyTwo(1)) == comptime_int);
    const y: i64 = 2;
    try expect(addFortyTwo(y) == 44);
    try expect(@TypeOf(addFortyTwo(y)) == i64);
}

$ zig test test_fn_type_inference.zig
1/1 test_fn_type_inference.test.fn type inference...OK
All 1 tests passed.

test "inline function call" {
    if (foo(1200, 34) != 1234) {
        @compileError("bad");
    }
}

inline fn foo(a: i32, b: i32) i32 {
    return a + b;
}

$ zig test inline_call.zig
1/1 inline_call.test.inline function call...OK
All 1 tests passed.

const std = @import("std");
const math = std.math;
const testing = std.testing;

test "fn reflection" {
    try testing.expect(@typeInfo(@TypeOf(testing.expect)).Fn.params[0].type.? == bool);
    try testing.expect(@typeInfo(@TypeOf(testing.tmpDir)).Fn.return_type.? == testing.TmpDir);

    try testing.expect(@typeInfo(@TypeOf(math.Log2Int)).Fn.is_generic);
}

$ zig test test_fn_reflection.zig
1/1 test_fn_reflection.test.fn reflection...OK
All 1 tests passed.

const std = @import("std");

const FileOpenError = error{
    AccessDenied,
    OutOfMemory,
    FileNotFound,
};

const AllocationError = error{
    OutOfMemory,
};

test "coerce subset to superset" {
    const err = foo(AllocationError.OutOfMemory);
    try std.testing.expect(err == FileOpenError.OutOfMemory);
}

fn foo(err: AllocationError) FileOpenError {
    return err;
}

$ zig test test_coerce_error_subset_to_superset.zig
1/1 test_coerce_error_subset_to_superset.test.coerce subset to superset...OK
All 1 tests passed.

const FileOpenError = error{
    AccessDenied,
    OutOfMemory,
    FileNotFound,
};

const AllocationError = error{
    OutOfMemory,
};

test "coerce superset to subset" {
    foo(FileOpenError.OutOfMemory) catch {};
}

fn foo(err: FileOpenError) AllocationError {
    return err;
}

$ zig test test_coerce_error_superset_to_subset.zig
doc/langref/test_coerce_error_superset_to_subset.zig:16:12: error: expected type 'error{OutOfMemory}', found 'error{AccessDenied,OutOfMemory,FileNotFound}'
    return err;
           ^~~
doc/langref/test_coerce_error_superset_to_subset.zig:16:12: note: 'error.AccessDenied' not a member of destination error set
doc/langref/test_coerce_error_superset_to_subset.zig:16:12: note: 'error.FileNotFound' not a member of destination error set
doc/langref/test_coerce_error_superset_to_subset.zig:15:28: note: function return type declared here
fn foo(err: FileOpenError) AllocationError {
                           ^~~~~~~~~~~~~~~
referenced by:
    test.coerce superset to subset: doc/langref/test_coerce_error_superset_to_subset.zig:12:5
    remaining reference traces hidden; use '-freference-trace' to see all reference traces

const err = error.FileNotFound;

const err = (error{FileNotFound}).FileNotFound;

const std = @import("std");
const maxInt = std.math.maxInt;

pub fn parseU64(buf: []const u8, radix: u8) !u64 {
    var x: u64 = 0;

    for (buf) |c| {
        const digit = charToDigit(c);

        if (digit >= radix) {
            return error.InvalidChar;
        }

        // x *= radix
        var ov = @mulWithOverflow(x, radix);
        if (ov[1] != 0) return error.OverFlow;

        // x += digit
        ov = @addWithOverflow(ov[0], digit);
        if (ov[1] != 0) return error.OverFlow;
        x = ov[0];
    }

    return x;
}

fn charToDigit(c: u8) u8 {
    return switch (c) {
        '0'...'9' => c - '0',
        'A'...'Z' => c - 'A' + 10,
        'a'...'z' => c - 'a' + 10,
        else => maxInt(u8),
    };
}

test "parse u64" {
    const result = try parseU64("1234", 10);
    try std.testing.expect(result == 1234);
}

$ zig test error_union_parsing_u64.zig
1/1 error_union_parsing_u64.test.parse u64...OK
All 1 tests passed.

const parseU64 = @import("error_union_parsing_u64.zig").parseU64;

fn doAThing(str: []u8) void {
    const number = parseU64(str, 10) catch 13;
    _ = number; // ...
}

const parseU64 = @import("error_union_parsing_u64.zig").parseU64;

fn doAThing(str: []u8) void {
    const number = parseU64(str, 10) catch blk: {
        // do things
        break :blk 13;
    };
    _ = number; // number is now initialized
}

const parseU64 = @import("error_union_parsing_u64.zig").parseU64;

fn doAThing(str: []u8) !void {
    const number = parseU64(str, 10) catch |err| return err;
    _ = number; // ...
}

const parseU64 = @import("error_union_parsing_u64.zig").parseU64;

fn doAThing(str: []u8) !void {
    const number = try parseU64(str, 10);
    _ = number; // ...
}

fn doAThing(str: []u8) void {
    if (parseU64(str, 10)) |number| {
        doSomethingWithNumber(number);
    } else |err| switch (err) {
        error.Overflow => {
            // handle overflow...
        },
        // we promise that InvalidChar won't happen (or crash in debug mode if it does)
        error.InvalidChar => unreachable,
    }
}

fn doAnotherThing(str: []u8) error{InvalidChar}!void {
    if (parseU64(str, 10)) |number| {
        doSomethingWithNumber(number);
    } else |err| switch (err) {
        error.Overflow => {
            // handle overflow...
        },
        else => |leftover_err| return leftover_err,
    }
}

fn doADifferentThing(str: []u8) void {
    if (parseU64(str, 10)) |number| {
        doSomethingWithNumber(number);
    } else |_| {
        // do as you'd like
    }
}

fn createFoo(param: i32) !Foo {
    const foo = try tryToAllocateFoo();
    // now we have allocated foo. we need to free it if the function fails.
    // but we want to return it if the function succeeds.
    errdefer deallocateFoo(foo);

    const tmp_buf = allocateTmpBuffer() orelse return error.OutOfMemory;
    // tmp_buf is truly a temporary resource, and we for sure want to clean it up
    // before this block leaves scope
    defer deallocateTmpBuffer(tmp_buf);

    if (param > 1337) return error.InvalidParam;

    // here the errdefer will not run since we're returning success from the function.
    // but the defer will run!
    return foo;
}

const std = @import("std");
const Allocator = std.mem.Allocator;

const Foo = struct {
    data: u32,
};

fn tryToAllocateFoo(allocator: Allocator) !*Foo {
    return allocator.create(Foo);
}

fn deallocateFoo(allocator: Allocator, foo: *Foo) void {
    allocator.destroy(foo);
}

fn getFooData() !u32 {
    return 666;
}

fn createFoo(allocator: Allocator, param: i32) !*Foo {
    const foo = getFoo: {
        var foo = try tryToAllocateFoo(allocator);
        errdefer deallocateFoo(allocator, foo); // Only lasts until the end of getFoo

        // Calls deallocateFoo on error
        foo.data = try getFooData();

        break :getFoo foo;
    };

    // Outside of the scope of the errdefer, so
    // deallocateFoo will not be called here
    if (param > 1337) return error.InvalidParam;

    return foo;
}

test "createFoo" {
    try std.testing.expectError(error.InvalidParam, createFoo(std.testing.allocator, 2468));
}

$ zig test test_errdefer_slip_ups.zig
1/1 test_errdefer_slip_ups.test.createFoo...OK
[gpa] (err): memory address 0x7f11f521a000 leaked:
/home/andy/src/zig/doc/langref/test_errdefer_slip_ups.zig:9:28: 0x103d3cf in tryToAllocateFoo (test)
    return allocator.create(Foo);
                           ^
/home/andy/src/zig/doc/langref/test_errdefer_slip_ups.zig:22:39: 0x103d5e5 in createFoo (test)
        var foo = try tryToAllocateFoo(allocator);
                                      ^
/home/andy/src/zig/doc/langref/test_errdefer_slip_ups.zig:39:62: 0x103d82d in test.createFoo (test)
    try std.testing.expectError(error.InvalidParam, createFoo(std.testing.allocator, 2468));
                                                             ^
/home/andy/src/zig/lib/compiler/test_runner.zig:157:25: 0x104d2a0 in mainTerminal (test)
        if (test_fn.func()) |_| {
                        ^
/home/andy/src/zig/lib/compiler/test_runner.zig:37:28: 0x104340b in main (test)
        return mainTerminal();
                           ^
/home/andy/src/zig/lib/std/start.zig:514:22: 0x103f9f9 in posixCallMainAndExit (test)
            root.main();
                     ^
/home/andy/src/zig/lib/std/start.zig:266:5: 0x103f561 in _start (test)
    asm volatile (switch (native_arch) {
    ^

All 1 tests passed.
1 errors were logged.
1 tests leaked memory.
error: the following test command failed with exit code 1:
/home/andy/src/zig/.zig-cache/o/58c079cb550addefaa354f72d736afd7/test

const std = @import("std");
const Allocator = std.mem.Allocator;

const Foo = struct {
    data: u32,
};

fn tryToAllocateFoo(allocator: Allocator) !*Foo {
    return allocator.create(Foo);
}

fn deallocateFoo(allocator: Allocator, foo: *Foo) void {
    allocator.destroy(foo);
}

fn getFooData() !u32 {
    return 666;
}

fn createFoo(allocator: Allocator, param: i32) !*Foo {
    const foo = getFoo: {
        var foo = try tryToAllocateFoo(allocator);
        errdefer deallocateFoo(allocator, foo);

        foo.data = try getFooData();

        break :getFoo foo;
    };
    // This lasts for the rest of the function
    errdefer deallocateFoo(allocator, foo);

    // Error is now properly handled by errdefer
    if (param > 1337) return error.InvalidParam;

    return foo;
}

test "createFoo" {
    try std.testing.expectError(error.InvalidParam, createFoo(std.testing.allocator, 2468));
}

$ zig test test_errdefer_block.zig
1/1 test_errdefer_block.test.createFoo...OK
All 1 tests passed.

const std = @import("std");
const Allocator = std.mem.Allocator;

const Foo = struct { data: *u32 };

fn getData() !u32 {
    return 666;
}

fn genFoos(allocator: Allocator, num: usize) ![]Foo {
    const foos = try allocator.alloc(Foo, num);
    errdefer allocator.free(foos);

    for (foos, 0..) |*foo, i| {
        foo.data = try allocator.create(u32);
        // This errdefer does not last between iterations
        errdefer allocator.destroy(foo.data);

        // The data for the first 3 foos will be leaked
        if (i >= 3) return error.TooManyFoos;

        foo.data.* = try getData();
    }

    return foos;
}

test "genFoos" {
    try std.testing.expectError(error.TooManyFoos, genFoos(std.testing.allocator, 5));
}

$ zig test test_errdefer_loop_leak.zig
1/1 test_errdefer_loop_leak.test.genFoos...OK
[gpa] (err): memory address 0x7f57c7578000 leaked:
/home/andy/src/zig/doc/langref/test_errdefer_loop_leak.zig:15:40: 0x103d7a6 in genFoos (test)
        foo.data = try allocator.create(u32);
                                       ^
/home/andy/src/zig/doc/langref/test_errdefer_loop_leak.zig:29:59: 0x103e0dd in test.genFoos (test)
    try std.testing.expectError(error.TooManyFoos, genFoos(std.testing.allocator, 5));
                                                          ^
/home/andy/src/zig/lib/compiler/test_runner.zig:157:25: 0x104e010 in mainTerminal (test)
        if (test_fn.func()) |_| {
                        ^
/home/andy/src/zig/lib/compiler/test_runner.zig:37:28: 0x1043eab in main (test)
        return mainTerminal();
                           ^
/home/andy/src/zig/lib/std/start.zig:514:22: 0x10402a9 in posixCallMainAndExit (test)
            root.main();
                     ^
/home/andy/src/zig/lib/std/start.zig:266:5: 0x103fe11 in _start (test)
    asm volatile (switch (native_arch) {
    ^

[gpa] (err): memory address 0x7f57c7578004 leaked:
/home/andy/src/zig/doc/langref/test_errdefer_loop_leak.zig:15:40: 0x103d7a6 in genFoos (test)
        foo.data = try allocator.create(u32);
                                       ^
/home/andy/src/zig/doc/langref/test_errdefer_loop_leak.zig:29:59: 0x103e0dd in test.genFoos (test)
    try std.testing.expectError(error.TooManyFoos, genFoos(std.testing.allocator, 5));
                                                          ^
/home/andy/src/zig/lib/compiler/test_runner.zig:157:25: 0x104e010 in mainTerminal (test)
        if (test_fn.func()) |_| {
                        ^
/home/andy/src/zig/lib/compiler/test_runner.zig:37:28: 0x1043eab in main (test)
        return mainTerminal();
                           ^
/home/andy/src/zig/lib/std/start.zig:514:22: 0x10402a9 in posixCallMainAndExit (test)
            root.main();
                     ^
/home/andy/src/zig/lib/std/start.zig:266:5: 0x103fe11 in _start (test)
    asm volatile (switch (native_arch) {
    ^

[gpa] (err): memory address 0x7f57c7578008 leaked:
/home/andy/src/zig/doc/langref/test_errdefer_loop_leak.zig:15:40: 0x103d7a6 in genFoos (test)
        foo.data = try allocator.create(u32);
                                       ^
/home/andy/src/zig/doc/langref/test_errdefer_loop_leak.zig:29:59: 0x103e0dd in test.genFoos (test)
    try std.testing.expectError(error.TooManyFoos, genFoos(std.testing.allocator, 5));
                                                          ^
/home/andy/src/zig/lib/compiler/test_runner.zig:157:25: 0x104e010 in mainTerminal (test)
        if (test_fn.func()) |_| {
                        ^
/home/andy/src/zig/lib/compiler/test_runner.zig:37:28: 0x1043eab in main (test)
        return mainTerminal();
                           ^
/home/andy/src/zig/lib/std/start.zig:514:22: 0x10402a9 in posixCallMainAndExit (test)
            root.main();
                     ^
/home/andy/src/zig/lib/std/start.zig:266:5: 0x103fe11 in _start (test)
    asm volatile (switch (native_arch) {
    ^

All 1 tests passed.
3 errors were logged.
1 tests leaked memory.
error: the following test command failed with exit code 1:
/home/andy/src/zig/.zig-cache/o/29fcda275b7c426418534b679850fa2e/test

const std = @import("std");
const Allocator = std.mem.Allocator;

const Foo = struct { data: *u32 };

fn getData() !u32 {
    return 666;
}

fn genFoos(allocator: Allocator, num: usize) ![]Foo {
    const foos = try allocator.alloc(Foo, num);
    errdefer allocator.free(foos);

    // Used to track how many foos have been initialized
    // (including their data being allocated)
    var num_allocated: usize = 0;
    errdefer for (foos[0..num_allocated]) |foo| {
        allocator.destroy(foo.data);
    };
    for (foos, 0..) |*foo, i| {
        foo.data = try allocator.create(u32);
        num_allocated += 1;

        if (i >= 3) return error.TooManyFoos;

        foo.data.* = try getData();
    }

    return foos;
}

test "genFoos" {
    try std.testing.expectError(error.TooManyFoos, genFoos(std.testing.allocator, 5));
}

$ zig test test_errdefer_loop.zig
1/1 test_errdefer_loop.test.genFoos...OK
All 1 tests passed.

const expect = @import("std").testing.expect;

test "error union" {
    var foo: anyerror!i32 = undefined;

    // Coerce from child type of an error union:
    foo = 1234;

    // Coerce from an error set:
    foo = error.SomeError;

    // Use compile-time reflection to access the payload type of an error union:
    try comptime expect(@typeInfo(@TypeOf(foo)).ErrorUnion.payload == i32);

    // Use compile-time reflection to access the error set type of an error union:
    try comptime expect(@typeInfo(@TypeOf(foo)).ErrorUnion.error_set == anyerror);
}

$ zig test test_error_union.zig
1/1 test_error_union.test.error union...OK
All 1 tests passed.

const A = error{
    NotDir,

    /// A doc comment
    PathNotFound,
};
const B = error{
    OutOfMemory,

    /// B doc comment
    PathNotFound,
};

const C = A || B;

fn foo() C!void {
    return error.NotDir;
}

test "merge error sets" {
    if (foo()) {
        @panic("unexpected");
    } else |err| switch (err) {
        error.OutOfMemory => @panic("unexpected"),
        error.PathNotFound => @panic("unexpected"),
        error.NotDir => {},
    }
}

$ zig test test_merging_error_sets.zig
1/1 test_merging_error_sets.test.merge error sets...OK
All 1 tests passed.

// With an inferred error set
pub fn add_inferred(comptime T: type, a: T, b: T) !T {
    const ov = @addWithOverflow(a, b);
    if (ov[1] != 0) return error.Overflow;
    return ov[0];
}

// With an explicit error set
pub fn add_explicit(comptime T: type, a: T, b: T) Error!T {
    const ov = @addWithOverflow(a, b);
    if (ov[1] != 0) return error.Overflow;
    return ov[0];
}

const Error = error{
    Overflow,
};

const std = @import("std");

test "inferred error set" {
    if (add_inferred(u8, 255, 1)) |_| unreachable else |err| switch (err) {
        error.Overflow => {}, // ok
    }
}

$ zig test test_inferred_error_sets.zig
1/1 test_inferred_error_sets.test.inferred error set...OK
All 1 tests passed.

pub fn main() !void {
    try foo(12);
}

fn foo(x: i32) !void {
    if (x >= 5) {
        try bar();
    } else {
        try bang2();
    }
}

fn bar() !void {
    if (baz()) {
        try quux();
    } else |err| switch (err) {
        error.FileNotFound => try hello(),
    }
}

fn baz() !void {
    try bang1();
}

fn quux() !void {
    try bang2();
}

fn hello() !void {
    try bang2();
}

fn bang1() !void {
    return error.FileNotFound;
}

fn bang2() !void {
    return error.PermissionDenied;
}

$ zig build-exe error_return_trace.zig
$ ./error_return_trace
error: PermissionDenied
/home/andy/src/zig/doc/langref/error_return_trace.zig:34:5: 0x1034e08 in bang1 (error_return_trace)
    return error.FileNotFound;
    ^
/home/andy/src/zig/doc/langref/error_return_trace.zig:22:5: 0x1034f13 in baz (error_return_trace)
    try bang1();
    ^
/home/andy/src/zig/doc/langref/error_return_trace.zig:38:5: 0x1034f38 in bang2 (error_return_trace)
    return error.PermissionDenied;
    ^
/home/andy/src/zig/doc/langref/error_return_trace.zig:30:5: 0x1034fa3 in hello (error_return_trace)
    try bang2();
    ^
/home/andy/src/zig/doc/langref/error_return_trace.zig:17:31: 0x103505a in bar (error_return_trace)
        error.FileNotFound => try hello(),
                              ^
/home/andy/src/zig/doc/langref/error_return_trace.zig:7:9: 0x1035140 in foo (error_return_trace)
        try bar();
        ^
/home/andy/src/zig/doc/langref/error_return_trace.zig:2:5: 0x1035198 in main (error_return_trace)
    try foo(12);
    ^

pub fn main() void {
    foo(12);
}

fn foo(x: i32) void {
    if (x >= 5) {
        bar();
    } else {
        bang2();
    }
}

fn bar() void {
    if (baz()) {
        quux();
    } else {
        hello();
    }
}

fn baz() bool {
    return bang1();
}

fn quux() void {
    bang2();
}

fn hello() void {
    bang2();
}

fn bang1() bool {
    return false;
}

fn bang2() void {
    @panic("PermissionDenied");
}

$ zig build-exe stack_trace.zig
$ ./stack_trace
thread 3570764 panic: PermissionDenied
/home/andy/src/zig/doc/langref/stack_trace.zig:38:5: 0x1039320 in bang2 (stack_trace)
    @panic("PermissionDenied");
    ^
/home/andy/src/zig/doc/langref/stack_trace.zig:30:10: 0x1068bd8 in hello (stack_trace)
    bang2();
         ^
/home/andy/src/zig/doc/langref/stack_trace.zig:17:14: 0x10392fc in bar (stack_trace)
        hello();
             ^
/home/andy/src/zig/doc/langref/stack_trace.zig:7:12: 0x103721c in foo (stack_trace)
        bar();
           ^
/home/andy/src/zig/doc/langref/stack_trace.zig:2:8: 0x103519d in main (stack_trace)
    foo(12);
       ^
/home/andy/src/zig/lib/std/start.zig:514:22: 0x1034a49 in posixCallMainAndExit (stack_trace)
            root.main();
                     ^
/home/andy/src/zig/lib/std/start.zig:266:5: 0x10345b1 in _start (stack_trace)
    asm volatile (switch (native_arch) {
    ^
???:?:?: 0x0 in ??? (???)
(process terminated by signal)

pub const StackTrace = struct {
    index: usize,
    instruction_addresses: [N]usize,
};

// marked as "no-inline" in LLVM IR
fn __zig_return_error(stack_trace: *StackTrace) void {
    stack_trace.instruction_addresses[stack_trace.index] = @returnAddress();
    stack_trace.index = (stack_trace.index + 1) % N;
}

// normal integer
const normal_int: i32 = 1234;

// optional integer
const optional_int: ?i32 = 5678;

// malloc prototype included for reference
void *malloc(size_t size);

struct Foo *do_a_thing(void) {
    char *ptr = malloc(1234);
    if (!ptr) return NULL;
    // ...
}

// malloc prototype included for reference
extern fn malloc(size: usize) ?[*]u8;

fn doAThing() ?*Foo {
    const ptr = malloc(1234) orelse return null;
    _ = ptr; // ...
}

void do_a_thing(struct Foo *foo) {
    // do some stuff

    if (foo) {
        do_something_with_foo(foo);
    }

    // do some stuff
}

const Foo = struct {};
fn doSomethingWithFoo(foo: *Foo) void {
    _ = foo;
}

fn doAThing(optional_foo: ?*Foo) void {
    // do some stuff

    if (optional_foo) |foo| {
        doSomethingWithFoo(foo);
    }

    // do some stuff
}

const expect = @import("std").testing.expect;

test "optional type" {
    // Declare an optional and coerce from null:
    var foo: ?i32 = null;

    // Coerce from child type of an optional
    foo = 1234;

    // Use compile-time reflection to access the child type of the optional:
    try comptime expect(@typeInfo(@TypeOf(foo)).Optional.child == i32);
}

$ zig test test_optional_type.zig
1/1 test_optional_type.test.optional type...OK
All 1 tests passed.

const optional_value: ?i32 = null;

const expect = @import("std").testing.expect;

test "optional pointers" {
    // Pointers cannot be null. If you want a null pointer, use the optional
    // prefix `?` to make the pointer type optional.
    var ptr: ?*i32 = null;

    var x: i32 = 1;
    ptr = &x;

    try expect(ptr.?.* == 1);

    // Optional pointers are the same size as normal pointers, because pointer
    // value 0 is used as the null value.
    try expect(@sizeOf(?*i32) == @sizeOf(*i32));
}

$ zig test test_optional_pointer.zig
1/1 test_optional_pointer.test.optional pointers...OK
All 1 tests passed.

test "type coercion - variable declaration" {
    const a: u8 = 1;
    const b: u16 = a;
    _ = b;
}

test "type coercion - function call" {
    const a: u8 = 1;
    foo(a);
}

fn foo(b: u16) void {
    _ = b;
}

test "type coercion - @as builtin" {
    const a: u8 = 1;
    const b = @as(u16, a);
    _ = b;
}

$ zig test test_type_coercion.zig
1/3 test_type_coercion.test.type coercion - variable declaration...OK
2/3 test_type_coercion.test.type coercion - function call...OK
3/3 test_type_coercion.test.type coercion - @as builtin...OK
All 3 tests passed.

test "type coercion - const qualification" {
    var a: i32 = 1;
    const b: *i32 = &a;
    foo(b);
}

fn foo(_: *const i32) void {}

$ zig test test_no_op_casts.zig
1/1 test_no_op_casts.test.type coercion - const qualification...OK
All 1 tests passed.

const std = @import("std");
const expect = std.testing.expect;
const mem = std.mem;

test "cast *[1][*]const u8 to [*]const ?[*]const u8" {
    const window_name = [1][*]const u8{"window name"};
    const x: [*]const ?[*]const u8 = &window_name;
    try expect(mem.eql(u8, std.mem.sliceTo(@as([*:0]const u8, @ptrCast(x[0].?)), 0), "window name"));
}

$ zig test test_pointer_coerce_const_optional.zig
1/1 test_pointer_coerce_const_optional.test.cast *[1][*]const u8 to [*]const ?[*]const u8...OK
All 1 tests passed.

const std = @import("std");
const builtin = @import("builtin");
const expect = std.testing.expect;
const mem = std.mem;

test "integer widening" {
    const a: u8 = 250;
    const b: u16 = a;
    const c: u32 = b;
    const d: u64 = c;
    const e: u64 = d;
    const f: u128 = e;
    try expect(f == a);
}

test "implicit unsigned integer to signed integer" {
    const a: u8 = 250;
    const b: i16 = a;
    try expect(b == 250);
}

test "float widening" {
    const a: f16 = 12.34;
    const b: f32 = a;
    const c: f64 = b;
    const d: f128 = c;
    try expect(d == a);
}

$ zig test test_integer_widening.zig
1/3 test_integer_widening.test.integer widening...OK
2/3 test_integer_widening.test.implicit unsigned integer to signed integer...OK
3/3 test_integer_widening.test.float widening...OK
All 3 tests passed.

// Compile time coercion of float to int
test "implicit cast to comptime_int" {
    const f: f32 = 54.0 / 5;
    _ = f;
}

$ zig test test_ambiguous_coercion.zig
doc/langref/test_ambiguous_coercion.zig:3:25: error: ambiguous coercion of division operands 'comptime_float' and 'comptime_int'; non-zero remainder '4'
    const f: f32 = 54.0 / 5;
                   ~~~~~^~~

const std = @import("std");
const expect = std.testing.expect;

// You can assign constant pointers to arrays to a slice with
// const modifier on the element type. Useful in particular for
// String literals.
test "*const [N]T to []const T" {
    const x1: []const u8 = "hello";
    const x2: []const u8 = &[5]u8{ 'h', 'e', 'l', 'l', 111 };
    try expect(std.mem.eql(u8, x1, x2));

    const y: []const f32 = &[2]f32{ 1.2, 3.4 };
    try expect(y[0] == 1.2);
}

// Likewise, it works when the destination type is an error union.
test "*const [N]T to E![]const T" {
    const x1: anyerror![]const u8 = "hello";
    const x2: anyerror![]const u8 = &[5]u8{ 'h', 'e', 'l', 'l', 111 };
    try expect(std.mem.eql(u8, try x1, try x2));

    const y: anyerror![]const f32 = &[2]f32{ 1.2, 3.4 };
    try expect((try y)[0] == 1.2);
}

// Likewise, it works when the destination type is an optional.
test "*const [N]T to ?[]const T" {
    const x1: ?[]const u8 = "hello";
    const x2: ?[]const u8 = &[5]u8{ 'h', 'e', 'l', 'l', 111 };
    try expect(std.mem.eql(u8, x1.?, x2.?));

    const y: ?[]const f32 = &[2]f32{ 1.2, 3.4 };
    try expect(y.?[0] == 1.2);
}

// In this cast, the array length becomes the slice length.
test "*[N]T to []T" {
    var buf: [5]u8 = "hello".*;
    const x: []u8 = &buf;
    try expect(std.mem.eql(u8, x, "hello"));

    const buf2 = [2]f32{ 1.2, 3.4 };
    const x2: []const f32 = &buf2;
    try expect(std.mem.eql(f32, x2, &[2]f32{ 1.2, 3.4 }));
}

// Single-item pointers to arrays can be coerced to many-item pointers.
test "*[N]T to [*]T" {
    var buf: [5]u8 = "hello".*;
    const x: [*]u8 = &buf;
    try expect(x[4] == 'o');
    // x[5] would be an uncaught out of bounds pointer dereference!
}

// Likewise, it works when the destination type is an optional.
test "*[N]T to ?[*]T" {
    var buf: [5]u8 = "hello".*;
    const x: ?[*]u8 = &buf;
    try expect(x.?[4] == 'o');
}

// Single-item pointers can be cast to len-1 single-item arrays.
test "*T to *[1]T" {
    var x: i32 = 1234;
    const y: *[1]i32 = &x;
    const z: [*]i32 = y;
    try expect(z[0] == 1234);
}

$ zig test test_coerce_slices_arrays_and_pointers.zig
1/7 test_coerce_slices_arrays_and_pointers.test.*const [N]T to []const T...OK
2/7 test_coerce_slices_arrays_and_pointers.test.*const [N]T to E![]const T...OK
3/7 test_coerce_slices_arrays_and_pointers.test.*const [N]T to ?[]const T...OK
4/7 test_coerce_slices_arrays_and_pointers.test.*[N]T to []T...OK
5/7 test_coerce_slices_arrays_and_pointers.test.*[N]T to [*]T...OK
6/7 test_coerce_slices_arrays_and_pointers.test.*[N]T to ?[*]T...OK
7/7 test_coerce_slices_arrays_and_pointers.test.*T to *[1]T...OK
All 7 tests passed.

const std = @import("std");
const expect = std.testing.expect;

test "coerce to optionals" {
    const x: ?i32 = 1234;
    const y: ?i32 = null;

    try expect(x.? == 1234);
    try expect(y == null);
}

$ zig test test_coerce_optionals.zig
1/1 test_coerce_optionals.test.coerce to optionals...OK
All 1 tests passed.

const std = @import("std");
const expect = std.testing.expect;

test "coerce to optionals wrapped in error union" {
    const x: anyerror!?i32 = 1234;
    const y: anyerror!?i32 = null;

    try expect((try x).? == 1234);
    try expect((try y) == null);
}

$ zig test test_coerce_optional_wrapped_error_union.zig
1/1 test_coerce_optional_wrapped_error_union.test.coerce to optionals wrapped in error union...OK
All 1 tests passed.

const std = @import("std");
const expect = std.testing.expect;

test "coercion to error unions" {
    const x: anyerror!i32 = 1234;
    const y: anyerror!i32 = error.Failure;

    try expect((try x) == 1234);
    try std.testing.expectError(error.Failure, y);
}

$ zig test test_coerce_to_error_union.zig
1/1 test_coerce_to_error_union.test.coercion to error unions...OK
All 1 tests passed.

const std = @import("std");
const expect = std.testing.expect;

test "coercing large integer type to smaller one when value is comptime-known to fit" {
    const x: u64 = 255;
    const y: u8 = x;
    try expect(y == 255);
}

$ zig test test_coerce_large_to_small.zig
1/1 test_coerce_large_to_small.test.coercing large integer type to smaller one when value is comptime-known to fit...OK
All 1 tests passed.

const std = @import("std");
const expect = std.testing.expect;

const E = enum {
    one,
    two,
    three,
};

const U = union(E) {
    one: i32,
    two: f32,
    three,
};

const U2 = union(enum) {
    a: void,
    b: f32,

    fn tag(self: U2) usize {
        switch (self) {
            .a => return 1,
            .b => return 2,
        }
    }
};

test "coercion between unions and enums" {
    const u = U{ .two = 12.34 };
    const e: E = u; // coerce union to enum
    try expect(e == E.two);

    const three = E.three;
    const u_2: U = three; // coerce enum to union
    try expect(u_2 == E.three);

    const u_3: U = .three; // coerce enum literal to union
    try expect(u_3 == E.three);

    const u_4: U2 = .a; // coerce enum literal to union with inferred enum tag type.
    try expect(u_4.tag() == 1);

    // The following example is invalid.
    // error: coercion from enum '@TypeOf(.enum_literal)' to union 'test_coerce_unions_enum.U2' must initialize 'f32' field 'b'
    //var u_5: U2 = .b;
    //try expect(u_5.tag() == 2);
}

$ zig test test_coerce_unions_enums.zig
1/1 test_coerce_unions_enums.test.coercion between unions and enums...OK
All 1 tests passed.

const std = @import("std");
const expect = std.testing.expect;

const Tuple = struct { u8, u8 };
test "coercion from homogenous tuple to array" {
    const tuple: Tuple = .{ 5, 6 };
    const array: [2]u8 = tuple;
    _ = array;
}

$ zig test test_coerce_tuples_arrays.zig
1/1 test_coerce_tuples_arrays.test.coercion from homogenous tuple to array...OK
All 1 tests passed.

const std = @import("std");
const expect = std.testing.expect;
const mem = std.mem;

test "peer resolve int widening" {
    const a: i8 = 12;
    const b: i16 = 34;
    const c = a + b;
    try expect(c == 46);
    try expect(@TypeOf(c) == i16);
}

test "peer resolve arrays of different size to const slice" {
    try expect(mem.eql(u8, boolToStr(true), "true"));
    try expect(mem.eql(u8, boolToStr(false), "false"));
    try comptime expect(mem.eql(u8, boolToStr(true), "true"));
    try comptime expect(mem.eql(u8, boolToStr(false), "false"));
}
fn boolToStr(b: bool) []const u8 {
    return if (b) "true" else "false";
}

test "peer resolve array and const slice" {
    try testPeerResolveArrayConstSlice(true);
    try comptime testPeerResolveArrayConstSlice(true);
}
fn testPeerResolveArrayConstSlice(b: bool) !void {
    const value1 = if (b) "aoeu" else @as([]const u8, "zz");
    const value2 = if (b) @as([]const u8, "zz") else "aoeu";
    try expect(mem.eql(u8, value1, "aoeu"));
    try expect(mem.eql(u8, value2, "zz"));
}

test "peer type resolution: ?T and T" {
    try expect(peerTypeTAndOptionalT(true, false).? == 0);
    try expect(peerTypeTAndOptionalT(false, false).? == 3);
    comptime {
        try expect(peerTypeTAndOptionalT(true, false).? == 0);
        try expect(peerTypeTAndOptionalT(false, false).? == 3);
    }
}
fn peerTypeTAndOptionalT(c: bool, b: bool) ?usize {
    if (c) {
        return if (b) null else @as(usize, 0);
    }

    return @as(usize, 3);
}

test "peer type resolution: *[0]u8 and []const u8" {
    try expect(peerTypeEmptyArrayAndSlice(true, "hi").len == 0);
    try expect(peerTypeEmptyArrayAndSlice(false, "hi").len == 1);
    comptime {
        try expect(peerTypeEmptyArrayAndSlice(true, "hi").len == 0);
        try expect(peerTypeEmptyArrayAndSlice(false, "hi").len == 1);
    }
}
fn peerTypeEmptyArrayAndSlice(a: bool, slice: []const u8) []const u8 {
    if (a) {
        return &[_]u8{};
    }

    return slice[0..1];
}
test "peer type resolution: *[0]u8, []const u8, and anyerror![]u8" {
    {
        var data = "hi".*;
        const slice = data[0..];
        try expect((try peerTypeEmptyArrayAndSliceAndError(true, slice)).len == 0);
        try expect((try peerTypeEmptyArrayAndSliceAndError(false, slice)).len == 1);
    }
    comptime {
        var data = "hi".*;
        const slice = data[0..];
        try expect((try peerTypeEmptyArrayAndSliceAndError(true, slice)).len == 0);
        try expect((try peerTypeEmptyArrayAndSliceAndError(false, slice)).len == 1);
    }
}
fn peerTypeEmptyArrayAndSliceAndError(a: bool, slice: []u8) anyerror![]u8 {
    if (a) {
        return &[_]u8{};
    }

    return slice[0..1];
}

test "peer type resolution: *const T and ?*T" {
    const a: *const usize = @ptrFromInt(0x123456780);
    const b: ?*usize = @ptrFromInt(0x123456780);
    try expect(a == b);
    try expect(b == a);
}

test "peer type resolution: error union switch" {
    // The non-error and error cases are only peers if the error case is just a switch expression;
    // the pattern `if (x) {...} else |err| blk: { switch (err) {...} }` does not consider the
    // non-error and error case to be peers.
    var a: error{ A, B, C }!u32 = 0;
    _ = &a;
    const b = if (a) |x|
        x + 3
    else |err| switch (err) {
        error.A => 0,
        error.B => 1,
        error.C => null,
    };
    try expect(@TypeOf(b) == ?u32);

    // The non-error and error cases are only peers if the error case is just a switch expression;
    // the pattern `x catch |err| blk: { switch (err) {...} }` does not consider the unwrapped `x`
    // and error case to be peers.
    const c = a catch |err| switch (err) {
        error.A => 0,
        error.B => 1,
        error.C => null,
    };
    try expect(@TypeOf(c) == ?u32);
}

$ zig test test_peer_type_resolution.zig
1/8 test_peer_type_resolution.test.peer resolve int widening...OK
2/8 test_peer_type_resolution.test.peer resolve arrays of different size to const slice...OK
3/8 test_peer_type_resolution.test.peer resolve array and const slice...OK
4/8 test_peer_type_resolution.test.peer type resolution: ?T and T...OK
5/8 test_peer_type_resolution.test.peer type resolution: *[0]u8 and []const u8...OK
6/8 test_peer_type_resolution.test.peer type resolution: *[0]u8, []const u8, and anyerror![]u8...OK
7/8 test_peer_type_resolution.test.peer type resolution: *const T and ?*T...OK
8/8 test_peer_type_resolution.test.peer type resolution: error union switch...OK
All 8 tests passed.

export fn entry() void {
    var x: void = {};
    var y: void = {};
    x = y;
    y = x;
}

const std = @import("std");
const expect = std.testing.expect;

test "turn HashMap into a set with void" {
    var map = std.AutoHashMap(i32, void).init(std.testing.allocator);
    defer map.deinit();

    try map.put(1, {});
    try map.put(2, {});

    try expect(map.contains(2));
    try expect(!map.contains(3));

    _ = map.remove(2);
    try expect(!map.contains(2));
}

$ zig test test_void_in_hashmap.zig
1/1 test_void_in_hashmap.test.turn HashMap into a set with void...OK
All 1 tests passed.

test "ignoring expression value" {
    foo();
}

fn foo() i32 {
    return 1234;
}

$ zig test test_expression_ignored.zig
doc/langref/test_expression_ignored.zig:2:8: error: value of type 'i32' ignored
    foo();
    ~~~^~
doc/langref/test_expression_ignored.zig:2:8: note: all non-void values must be used
doc/langref/test_expression_ignored.zig:2:8: note: to discard the value, assign it to '_'

test "void is ignored" {
    returnsVoid();
}

test "explicitly ignoring expression value" {
    _ = foo();
}

fn returnsVoid() void {}

fn foo() i32 {
    return 1234;
}

$ zig test test_void_ignored.zig
1/2 test_void_ignored.test.void is ignored...OK
2/2 test_void_ignored.test.explicitly ignoring expression value...OK
All 2 tests passed.

const expectEqual = @import("std").testing.expectEqual;
test "result type propagates through struct initializer" {
    const S = struct { x: u32 };
    const val: u64 = 123;
    const s: S = .{ .x = @intCast(val) };
    // .{ .x = @intCast(val) }   has result type `S` due to the type annotation
    //         @intCast(val)     has result type `u32` due to the type of the field `S.x`
    //                  val      has no result type, as it is permitted to be any integer type
    try expectEqual(@as(u32, 123), s.x);
}

$ zig test result_type_propagation.zig
1/1 result_type_propagation.test.result type propagates through struct initializer...OK
All 1 tests passed.

const expect = @import("std").testing.expect;
test "attempt to swap array elements with array initializer" {
    var arr: [2]u32 = .{ 1, 2 };
    arr = .{ arr[1], arr[0] };
    // The previous line is equivalent to the following two lines:
    //   arr[0] = arr[1];
    //   arr[1] = arr[0];
    // So this fails!
    try expect(arr[0] == 2); // succeeds
    try expect(arr[1] == 1); // fails
}

$ zig test result_location_interfering_with_swap.zig
1/1 result_location_interfering_with_swap.test.attempt to swap array elements with array initializer...FAIL (TestUnexpectedResult)
/home/andy/src/zig/lib/std/testing.zig:540:14: 0x103ce1f in expect (test)
    if (!ok) return error.TestUnexpectedResult;
             ^
/home/andy/src/zig/doc/langref/result_location_interfering_with_swap.zig:10:5: 0x103cf85 in test.attempt to swap array elements with array initializer (test)
    try expect(arr[1] == 1); // fails
    ^
0 passed; 0 skipped; 1 failed.
error: the following test command failed with exit code 1:
/home/andy/src/zig/.zig-cache/o/c42c6019fdf548f70655aafe3673a46e/test

test "using std namespace" {
    const S = struct {
        usingnamespace @import("std");
    };
    try S.testing.expect(true);
}

$ zig test test_usingnamespace.zig
1/1 test_usingnamespace.test.using std namespace...OK
All 1 tests passed.

pub usingnamespace @cImport({
    @cInclude("epoxy/gl.h");
    @cInclude("GLFW/glfw3.h");
    @cDefine("STBI_ONLY_PNG", "");
    @cDefine("STBI_NO_STDIO", "");
    @cInclude("stb_image.h");
});

fn max(comptime T: type, a: T, b: T) T {
    return if (a > b) a else b;
}
fn gimmeTheBiggerFloat(a: f32, b: f32) f32 {
    return max(f32, a, b);
}
fn gimmeTheBiggerInteger(a: u64, b: u64) u64 {
    return max(u64, a, b);
}

fn max(comptime T: type, a: T, b: T) T {
    return if (a > b) a else b;
}
test "try to pass a runtime type" {
    foo(false);
}
fn foo(condition: bool) void {
    const result = max(if (condition) f32 else u64, 1234, 5678);
    _ = result;
}

$ zig test test_unresolved_comptime_value.zig
doc/langref/test_unresolved_comptime_value.zig:8:28: error: unable to resolve comptime value
    const result = max(if (condition) f32 else u64, 1234, 5678);
                           ^~~~~~~~~
doc/langref/test_unresolved_comptime_value.zig:8:28: note: condition in comptime branch must be comptime-known
referenced by:
    test.try to pass a runtime type: doc/langref/test_unresolved_comptime_value.zig:5:5
    remaining reference traces hidden; use '-freference-trace' to see all reference traces

fn max(comptime T: type, a: T, b: T) T {
    return if (a > b) a else b;
}
test "try to compare bools" {
    _ = max(bool, true, false);
}

$ zig test test_comptime_mismatched_type.zig
doc/langref/test_comptime_mismatched_type.zig:2:18: error: operator > not allowed for type 'bool'
    return if (a > b) a else b;
               ~~^~~
referenced by:
    test.try to compare bools: doc/langref/test_comptime_mismatched_type.zig:5:12
    remaining reference traces hidden; use '-freference-trace' to see all reference traces

fn max(comptime T: type, a: T, b: T) T {
    if (T == bool) {
        return a or b;
    } else if (a > b) {
        return a;
    } else {
        return b;
    }
}
test "try to compare bools" {
    try @import("std").testing.expect(max(bool, false, true) == true);
}

$ zig test test_comptime_max_with_bool.zig
1/1 test_comptime_max_with_bool.test.try to compare bools...OK
All 1 tests passed.

fn max(a: bool, b: bool) bool {
    {
        return a or b;
    }
}

const expect = @import("std").testing.expect;

const CmdFn = struct {
    name: []const u8,
    func: fn (i32) i32,
};

const cmd_fns = [_]CmdFn{
    CmdFn{ .name = "one", .func = one },
    CmdFn{ .name = "two", .func = two },
    CmdFn{ .name = "three", .func = three },
};
fn one(value: i32) i32 {
    return value + 1;
}
fn two(value: i32) i32 {
    return value + 2;
}
fn three(value: i32) i32 {
    return value + 3;
}

fn performFn(comptime prefix_char: u8, start_value: i32) i32 {
    var result: i32 = start_value;
    comptime var i = 0;
    inline while (i < cmd_fns.len) : (i += 1) {
        if (cmd_fns[i].name[0] == prefix_char) {
            result = cmd_fns[i].func(result);
        }
    }
    return result;
}

test "perform fn" {
    try expect(performFn('t', 1) == 6);
    try expect(performFn('o', 0) == 1);
    try expect(performFn('w', 99) == 99);
}

$ zig test test_comptime_evaluation.zig
1/1 test_comptime_evaluation.test.perform fn...OK
All 1 tests passed.

// From the line:
// expect(performFn('t', 1) == 6);
fn performFn(start_value: i32) i32 {
    var result: i32 = start_value;
    result = two(result);
    result = three(result);
    return result;
}

// From the line:
// expect(performFn('o', 0) == 1);
fn performFn(start_value: i32) i32 {
    var result: i32 = start_value;
    result = one(result);
    return result;
}

// From the line:
// expect(performFn('w', 99) == 99);
fn performFn(start_value: i32) i32 {
    var result: i32 = start_value;
    _ = &result;
    return result;
}

extern fn exit() noreturn;

test "foo" {
    comptime {
        exit();
    }
}

$ zig test test_comptime_call_extern_function.zig
doc/langref/test_comptime_call_extern_function.zig:5:13: error: comptime call of extern function
        exit();
        ~~~~^~

const expect = @import("std").testing.expect;

fn fibonacci(index: u32) u32 {
    if (index < 2) return index;
    return fibonacci(index - 1) + fibonacci(index - 2);
}

test "fibonacci" {
    // test fibonacci at run-time
    try expect(fibonacci(7) == 13);

    // test fibonacci at compile-time
    try comptime expect(fibonacci(7) == 13);
}

$ zig test test_fibonacci_recursion.zig
1/1 test_fibonacci_recursion.test.fibonacci...OK
All 1 tests passed.

const expect = @import("std").testing.expect;

fn fibonacci(index: u32) u32 {
    //if (index < 2) return index;
    return fibonacci(index - 1) + fibonacci(index - 2);
}

test "fibonacci" {
    try comptime expect(fibonacci(7) == 13);
}

$ zig test test_fibonacci_comptime_overflow.zig
doc/langref/test_fibonacci_comptime_overflow.zig:5:28: error: overflow of integer type 'u32' with value '-1'
    return fibonacci(index - 1) + fibonacci(index - 2);
                     ~~~~~~^~~
doc/langref/test_fibonacci_comptime_overflow.zig:5:21: note: called from here (7 times)
    return fibonacci(index - 1) + fibonacci(index - 2);
           ~~~~~~~~~^~~~~~~~~~~
doc/langref/test_fibonacci_comptime_overflow.zig:9:34: note: called from here
    try comptime expect(fibonacci(7) == 13);
                        ~~~~~~~~~^~~

const assert = @import("std").debug.assert;

fn fibonacci(index: i32) i32 {
    //if (index < 2) return index;
    return fibonacci(index - 1) + fibonacci(index - 2);
}

test "fibonacci" {
    try comptime assert(fibonacci(7) == 13);
}

const assert = @import("std").debug.assert;

fn fibonacci(index: i32) i32 {
    if (index < 2) return index;
    return fibonacci(index - 1) + fibonacci(index - 2);
}

test "fibonacci" {
    try comptime assert(fibonacci(7) == 99999);
}

$ zig test test_fibonacci_comptime_unreachable.zig
lib/std/debug.zig:412:14: error: reached unreachable code
    if (!ok) unreachable; // assertion failure
             ^~~~~~~~~~~
doc/langref/test_fibonacci_comptime_unreachable.zig:9:24: note: called from here
    try comptime assert(fibonacci(7) == 99999);
                 ~~~~~~^~~~~~~~~~~~~~~~~~~~~~~

const first_25_primes = firstNPrimes(25);
const sum_of_first_25_primes = sum(&first_25_primes);

fn firstNPrimes(comptime n: usize) [n]i32 {
    var prime_list: [n]i32 = undefined;
    var next_index: usize = 0;
    var test_number: i32 = 2;
    while (next_index < prime_list.len) : (test_number += 1) {
        var test_prime_index: usize = 0;
        var is_prime = true;
        while (test_prime_index < next_index) : (test_prime_index += 1) {
            if (test_number % prime_list[test_prime_index] == 0) {
                is_prime = false;
                break;
            }
        }
        if (is_prime) {
            prime_list[next_index] = test_number;
            next_index += 1;
        }
    }
    return prime_list;
}

fn sum(numbers: []const i32) i32 {
    var result: i32 = 0;
    for (numbers) |x| {
        result += x;
    }
    return result;
}

test "variable values" {
    try @import("std").testing.expect(sum_of_first_25_primes == 1060);
}

$ zig test test_container-level_comptime_expressions.zig
1/1 test_container-level_comptime_expressions.test.variable values...OK
All 1 tests passed.

fn List(comptime T: type) type {
    return struct {
        items: []T,
        len: usize,
    };
}

// The generic List data structure can be instantiated by passing in a type:
var buffer: [10]i32 = undefined;
var list = List(i32){
    .items = &buffer,
    .len = 0,
};

const Node = struct {
    next: ?*Node,
    name: []const u8,
};

var node_a = Node{
    .next = null,
    .name = "Node A",
};

var node_b = Node{
    .next = &node_a,
    .name = "Node B",
};

const print = @import("std").debug.print;

const a_number: i32 = 1234;
const a_string = "foobar";

pub fn main() void {
    print("here is a string: '{s}' here is a number: {}\n", .{ a_string, a_number });
}

$ zig build-exe print.zig
$ ./print
here is a string: 'foobar' here is a number: 1234

const Writer = struct {
    /// Calls print and then flushes the buffer.
    pub fn print(self: *Writer, comptime format: []const u8, args: anytype) anyerror!void {
        const State = enum {
            start,
            open_brace,
            close_brace,
        };

        comptime var start_index: usize = 0;
        comptime var state = State.start;
        comptime var next_arg: usize = 0;

        inline for (format, 0..) |c, i| {
            switch (state) {
                State.start => switch (c) {
                    '{' => {
                        if (start_index < i) try self.write(format[start_index..i]);
                        state = State.open_brace;
                    },
                    '}' => {
                        if (start_index < i) try self.write(format[start_index..i]);
                        state = State.close_brace;
                    },
                    else => {},
                },
                State.open_brace => switch (c) {
                    '{' => {
                        state = State.start;
                        start_index = i;
                    },
                    '}' => {
                        try self.printValue(args[next_arg]);
                        next_arg += 1;
                        state = State.start;
                        start_index = i + 1;
                    },
                    's' => {
                        continue;
                    },
                    else => @compileError("Unknown format character: " ++ [1]u8{c}),
                },
                State.close_brace => switch (c) {
                    '}' => {
                        state = State.start;
                        start_index = i;
                    },
                    else => @compileError("Single '}' encountered in format string"),
                },
            }
        }
        comptime {
            if (args.len != next_arg) {
                @compileError("Unused arguments");
            }
            if (state != State.start) {
                @compileError("Incomplete format string: " ++ format);
            }
        }
        if (start_index < format.len) {
            try self.write(format[start_index..format.len]);
        }
        try self.flush();
    }

    fn write(self: *Writer, value: []const u8) !void {
        _ = self;
        _ = value;
    }
    pub fn printValue(self: *Writer, value: anytype) !void {
        _ = self;
        _ = value;
    }
    fn flush(self: *Writer) !void {
        _ = self;
    }
};

pub fn print(self: *Writer, arg0: []const u8, arg1: i32) !void {
    try self.write("here is a string: '");
    try self.printValue(arg0);
    try self.write("' here is a number: ");
    try self.printValue(arg1);
    try self.write("\n");
    try self.flush();
}

const Writer = struct {
    pub fn printValue(self: *Writer, value: anytype) !void {
        switch (@typeInfo(@TypeOf(value))) {
            .Int => {
                return self.writeInt(value);
            },
            .Float => {
                return self.writeFloat(value);
            },
            .Pointer => {
                return self.write(value);
            },
            else => {
                @compileError("Unable to print type '" ++ @typeName(@TypeOf(value)) ++ "'");
            },
        }
    }

    fn write(self: *Writer, value: []const u8) !void {
        _ = self;
        _ = value;
    }
    fn writeInt(self: *Writer, value: anytype) !void {
        _ = self;
        _ = value;
    }
    fn writeFloat(self: *Writer, value: anytype) !void {
        _ = self;
        _ = value;
    }
};

const print = @import("std").debug.print;

const a_number: i32 = 1234;
const a_string = "foobar";

test "print too many arguments" {
    print("here is a string: '{s}' here is a number: {}\n", .{
        a_string,
        a_number,
        a_number,
    });
}

$ zig test test_print_too_many_args.zig
lib/std/fmt.zig:203:18: error: unused argument in 'here is a string: '{s}' here is a number: {}
                               '
            1 => @compileError("unused argument in '" ++ fmt ++ "'"),
                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
referenced by:
    print__anon_2377: lib/std/io/Writer.zig:24:26
    print: lib/std/io.zig:324:47
    remaining reference traces hidden; use '-freference-trace' to see all reference traces

const print = @import("std").debug.print;

const a_number: i32 = 1234;
const a_string = "foobar";
const fmt = "here is a string: '{s}' here is a number: {}\n";

pub fn main() void {
    print(fmt, .{ a_string, a_number });
}

$ zig build-exe print_comptime-known_format.zig
$ ./print_comptime-known_format
here is a string: 'foobar' here is a number: 1234

pub fn main() noreturn {
    const msg = "hello world\n";
    _ = syscall3(SYS_write, STDOUT_FILENO, @intFromPtr(msg), msg.len);
    _ = syscall1(SYS_exit, 0);
    unreachable;
}

pub const SYS_write = 1;
pub const SYS_exit = 60;

pub const STDOUT_FILENO = 1;

pub fn syscall1(number: usize, arg1: usize) usize {
    return asm volatile ("syscall"
        : [ret] "={rax}" (-> usize),
        : [number] "{rax}" (number),
          [arg1] "{rdi}" (arg1),
        : "rcx", "r11"
    );
}

pub fn syscall3(number: usize, arg1: usize, arg2: usize, arg3: usize) usize {
    return asm volatile ("syscall"
        : [ret] "={rax}" (-> usize),
        : [number] "{rax}" (number),
          [arg1] "{rdi}" (arg1),
          [arg2] "{rsi}" (arg2),
          [arg3] "{rdx}" (arg3),
        : "rcx", "r11"
    );
}

$ zig build-exe inline_assembly.zig -target x86_64-linux
$ ./inline_assembly
hello world

pub fn syscall1(number: usize, arg1: usize) usize {
    // Inline assembly is an expression which returns a value.
    // the `asm` keyword begins the expression.
    return asm
    // `volatile` is an optional modifier that tells Zig this
    // inline assembly expression has side-effects. Without
    // `volatile`, Zig is allowed to delete the inline assembly
    // code if the result is unused.
    volatile (
    // Next is a comptime string which is the assembly code.
    // Inside this string one may use `%[ret]`, `%[number]`,
    // or `%[arg1]` where a register is expected, to specify
    // the register that Zig uses for the argument or return value,
    // if the register constraint strings are used. However in
    // the below code, this is not used. A literal `%` can be
    // obtained by escaping it with a double percent: `%%`.
    // Often multiline string syntax comes in handy here.
        \\syscall
        // Next is the output. It is possible in the future Zig will
        // support multiple outputs, depending on how
        // https://github.com/ziglang/zig/issues/215 is resolved.
        // It is allowed for there to be no outputs, in which case
        // this colon would be directly followed by the colon for the inputs.
        :
        // This specifies the name to be used in `%[ret]` syntax in
        // the above assembly string. This example does not use it,
        // but the syntax is mandatory.
          [ret]
          // Next is the output constraint string. This feature is still
          // considered unstable in Zig, and so LLVM/GCC documentation
          // must be used to understand the semantics.
          // http://releases.llvm.org/10.0.0/docs/LangRef.html#inline-asm-constraint-string
          // https://gcc.gnu.org/onlinedocs/gcc/Extended-Asm.html
          // In this example, the constraint string means "the result value of
          // this inline assembly instruction is whatever is in $rax".
          "={rax}"
          // Next is either a value binding, or `->` and then a type. The
          // type is the result type of the inline assembly expression.
          // If it is a value binding, then `%[ret]` syntax would be used
          // to refer to the register bound to the value.
          (-> usize),
          // Next is the list of inputs.
          // The constraint for these inputs means, "when the assembly code is
          // executed, $rax shall have the value of `number` and $rdi shall have
          // the value of `arg1`". Any number of input parameters is allowed,
          // including none.
        : [number] "{rax}" (number),
          [arg1] "{rdi}" (arg1),
          // Next is the list of clobbers. These declare a set of registers whose
          // values will not be preserved by the execution of this assembly code.
          // These do not include output or input registers. The special clobber
          // value of "memory" means that the assembly writes to arbitrary undeclared
          // memory locations - not only the memory pointed to by a declared indirect
          // output. In this example we list $rcx and $r11 because it is known the
          // kernel syscall does not preserve these registers.
        : "rcx", "r11"
    );
}

const std = @import("std");
const expect = std.testing.expect;

comptime {
    asm (
        \\.global my_func;
        \\.type my_func, @function;
        \\my_func:
        \\  lea (%rdi,%rsi,1),%eax
        \\  retq
    );
}

extern fn my_func(a: i32, b: i32) i32;

test "global assembly" {
    try expect(my_func(12, 34) == 46);
}

$ zig test test_global_assembly.zig -target x86_64-linux
1/1 test_global_assembly.test.global assembly...OK
All 1 tests passed.

const expect = @import("std").testing.expect;

test "noinline function call" {
    try expect(@call(.auto, add, .{ 3, 9 }) == 12);
}

fn add(a: i32, b: i32) i32 {
    return a + b;
}

$ zig test test_call_builtin.zig
1/1 test_call_builtin.test.noinline function call...OK
All 1 tests passed.

pub const CallModifier = enum {
    /// Equivalent to function call syntax.
    auto,

    /// Equivalent to async keyword used with function call syntax.
    async_kw,

    /// Prevents tail call optimization. This guarantees that the return
    /// address will point to the callsite, as opposed to the callsite's
    /// callsite. If the call is otherwise required to be tail-called
    /// or inlined, a compile error is emitted instead.
    never_tail,

    /// Guarantees that the call will not be inlined. If the call is
    /// otherwise required to be inlined, a compile error is emitted instead.
    never_inline,

    /// Asserts that the function call will not suspend. This allows a
    /// non-async function to call an async function.
    no_async,

    /// Guarantees that the call will be generated with tail call optimization.
    /// If this is not possible, a compile error is emitted instead.
    always_tail,

    /// Guarantees that the call will inlined at the callsite.
    /// If this is not possible, a compile error is emitted instead.
    always_inline,

    /// Evaluates the call at compile-time. If the call cannot be completed at
    /// compile-time, a compile error is emitted instead.
    compile_time,
};

fn cmpxchgStrongButNotAtomic(comptime T: type, ptr: *T, expected_value: T, new_value: T) ?T {
    const old_value = ptr.*;
    if (old_value == expected_value) {
        ptr.* = new_value;
        return null;
    } else {
        return old_value;
    }
}

fn cmpxchgWeakButNotAtomic(comptime T: type, ptr: *T, expected_value: T, new_value: T) ?T {
    const old_value = ptr.*;
    if (old_value == expected_value and usuallyTrueButSometimesFalse()) {
        ptr.* = new_value;
        return null;
    } else {
        return old_value;
    }
}

const print = @import("std").debug.print;

const num1 = blk: {
    var val1: i32 = 99;
    @compileLog("comptime val1 = ", val1);
    val1 = val1 + 1;
    break :blk val1;
};

test "main" {
    @compileLog("comptime in main");

    print("Runtime in main, num1 = {}.\n", .{num1});
}

$ zig test test_compileLog_builtin.zig
doc/langref/test_compileLog_builtin.zig:11:5: error: found compile log statement
    @compileLog("comptime in main");
    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
doc/langref/test_compileLog_builtin.zig:5:5: note: also here
    @compileLog("comptime val1 = ", val1);
    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Compile Log Output:
@as(*const [16:0]u8, "comptime in main")
@as(*const [16:0]u8, "comptime val1 = "), @as(i32, 99)

comptime {
    @export(internalName, .{ .name = "foo", .linkage = .strong });
}

fn internalName() callconv(.C) void {}

$ zig build-obj export_builtin.zig

export fn foo() void {}

$ zig build-obj export_builtin_equivalent_code.zig

export fn @"A function name that is a complete sentence."() void {}

$ zig build-obj export_any_symbol_name.zig

const std = @import("std");

const Point = struct {
    x: u32,
    y: u32,

    pub var z: u32 = 1;
};

test "field access by string" {
    const expect = std.testing.expect;
    var p = Point{ .x = 0, .y = 0 };

    @field(p, "x") = 4;
    @field(p, "y") = @field(p, "x") + 1;

    try expect(@field(p, "x") == 4);
    try expect(@field(p, "y") == 5);
}

test "decl access by string" {
    const expect = std.testing.expect;

    try expect(@field(Point, "z") == 1);

    @field(Point, "z") = 2;
    try expect(@field(Point, "z") == 2);
}

$ zig test test_field_builtin.zig
1/2 test_field_builtin.test.field access by string...OK
2/2 test_field_builtin.test.decl access by string...OK
All 2 tests passed.

const std = @import("std");
const expect = std.testing.expect;

const Foo = struct {
    nope: i32,

    pub var blah = "xxx";
    const hi = 1;
};

test "@hasDecl" {
    try expect(@hasDecl(Foo, "blah"));

    // Even though `hi` is private, @hasDecl returns true because this test is
    // in the same file scope as Foo. It would return false if Foo was declared
    // in a different file.
    try expect(@hasDecl(Foo, "hi"));

    // @hasDecl is for declarations; not fields.
    try expect(!@hasDecl(Foo, "nope"));
    try expect(!@hasDecl(Foo, "nope1234"));
}

$ zig test test_hasDecl_builtin.zig
1/1 test_hasDecl_builtin.test.@hasDecl...OK
All 1 tests passed.

test "integer cast panic" {
    var a: u16 = 0xabcd; // runtime-known
    _ = &a;
    const b: u8 = @intCast(a);
    _ = b;
}

$ zig test test_intCast_builtin.zig
1/1 test_intCast_builtin.test.integer cast panic...thread 3573820 panic: integer cast truncated bits
/home/andy/src/zig/doc/langref/test_intCast_builtin.zig:4:19: 0x103ce6b in test.integer cast panic (test)
    const b: u8 = @intCast(a);
                  ^
/home/andy/src/zig/lib/compiler/test_runner.zig:157:25: 0x1048290 in mainTerminal (test)
        if (test_fn.func()) |_| {
                        ^
/home/andy/src/zig/lib/compiler/test_runner.zig:37:28: 0x103e24b in main (test)
        return mainTerminal();
                           ^
/home/andy/src/zig/lib/std/start.zig:514:22: 0x103d389 in posixCallMainAndExit (test)
            root.main();
                     ^
/home/andy/src/zig/lib/std/start.zig:266:5: 0x103cef1 in _start (test)
    asm volatile (switch (native_arch) {
    ^
???:?:?: 0x0 in ??? (???)
error: the following test command crashed:
/home/andy/src/zig/.zig-cache/o/a3b6539437d55800e891e62090700351/test

const std = @import("std");
const native_arch = @import("builtin").target.cpu.arch;
const expect = std.testing.expect;

test "@wasmMemoryGrow" {
    if (native_arch != .wasm32) return error.SkipZigTest;

    const prev = @wasmMemorySize(0);
    try expect(prev == @wasmMemoryGrow(0, 1));
    try expect(prev + 1 == @wasmMemorySize(0));
}

$ zig test test_wasmMemoryGrow_builtin.zig
1/1 test_wasmMemoryGrow_builtin.test.@wasmMemoryGrow...SKIP
0 passed; 1 skipped; 0 failed.

test "foo" {
    comptime {
        var i = 0;
        while (i < 1001) : (i += 1) {}
    }
}

$ zig test test_without_setEvalBranchQuota_builtin.zig
doc/langref/test_without_setEvalBranchQuota_builtin.zig:4:9: error: evaluation exceeded 1000 backwards branches
        while (i < 1001) : (i += 1) {}
        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
doc/langref/test_without_setEvalBranchQuota_builtin.zig:4:9: note: use @setEvalBranchQuota() to raise the branch limit from 1000

test "foo" {
    comptime {
        @setEvalBranchQuota(1001);
        var i = 0;
        while (i < 1001) : (i += 1) {}
    }
}

$ zig test test_setEvalBranchQuota_builtin.zig
1/1 test_setEvalBranchQuota_builtin.test.foo...OK
All 1 tests passed.

test "@setRuntimeSafety" {
    // The builtin applies to the scope that it is called in. So here, integer overflow
    // will not be caught in ReleaseFast and ReleaseSmall modes:
    // var x: u8 = 255;
    // x += 1; // undefined behavior in ReleaseFast/ReleaseSmall modes.
    {
        // However this block has safety enabled, so safety checks happen here,
        // even in ReleaseFast and ReleaseSmall modes.
        @setRuntimeSafety(true);
        var x: u8 = 255;
        x += 1;

        {
            // The value can be overridden at any scope. So here integer overflow
            // would not be caught in any build mode.
            @setRuntimeSafety(false);
            // var x: u8 = 255;
            // x += 1; // undefined behavior in all build modes.
        }
    }
}

$ zig test test_setRuntimeSafety_builtin.zig -OReleaseFast
1/1 test_setRuntimeSafety_builtin.test.@setRuntimeSafety...thread 3579742 panic: integer overflow
/home/andy/src/zig/doc/langref/test_setRuntimeSafety_builtin.zig:11:11: 0x100ae54 in test.@setRuntimeSafety (test)
        x += 1;
          ^
/home/andy/src/zig/lib/compiler/test_runner.zig:157:25: 0x100c9b0 in main (test)
        if (test_fn.func()) |_| {
                        ^
/home/andy/src/zig/lib/std/start.zig:514:22: 0x100af44 in posixCallMainAndExit (test)
            root.main();
                     ^
/home/andy/src/zig/lib/std/start.zig:266:5: 0x100ae71 in _start (test)
    asm volatile (switch (native_arch) {
    ^
???:?:?: 0x0 in ??? (???)
error: the following test command crashed:
/home/andy/src/zig/.zig-cache/o/7c74a2939d84ddd0f45519d7a9f1c0f7/test

const std = @import("std");
const expect = std.testing.expect;

test "vector @shuffle" {
    const a = @Vector(7, u8){ 'o', 'l', 'h', 'e', 'r', 'z', 'w' };
    const b = @Vector(4, u8){ 'w', 'd', '!', 'x' };

    // To shuffle within a single vector, pass undefined as the second argument.
    // Notice that we can re-order, duplicate, or omit elements of the input vector
    const mask1 = @Vector(5, i32){ 2, 3, 1, 1, 0 };
    const res1: @Vector(5, u8) = @shuffle(u8, a, undefined, mask1);
    try expect(std.mem.eql(u8, &@as([5]u8, res1), "hello"));

    // Combining two vectors
    const mask2 = @Vector(6, i32){ -1, 0, 4, 1, -2, -3 };
    const res2: @Vector(6, u8) = @shuffle(u8, a, b, mask2);
    try expect(std.mem.eql(u8, &@as([6]u8, res2), "world!"));
}

$ zig test test_shuffle_builtin.zig
1/1 test_shuffle_builtin.test.vector @shuffle...OK
All 1 tests passed.

const std = @import("std");
const expect = std.testing.expect;

test "vector @splat" {
    const scalar: u32 = 5;
    const result: @Vector(4, u32) = @splat(scalar);
    try expect(std.mem.eql(u32, &@as([4]u32, result), &[_]u32{ 5, 5, 5, 5 }));
}

$ zig test test_splat_builtin.zig
1/1 test_splat_builtin.test.vector @splat...OK
All 1 tests passed.

const std = @import("std");
const expect = std.testing.expect;

test "vector @reduce" {
    const V = @Vector(4, i32);
    const value = V{ 1, -1, 1, -1 };
    const result = value > @as(V, @splat(0));
    // result is { true, false, true, false };
    try comptime expect(@TypeOf(result) == @Vector(4, bool));
    const is_all_true = @reduce(.And, result);
    try comptime expect(@TypeOf(is_all_true) == bool);
    try expect(is_all_true == false);
}

$ zig test test_reduce_builtin.zig
1/1 test_reduce_builtin.test.vector @reduce...OK
All 1 tests passed.

const std = @import("std");
const expect = std.testing.expect;

test "@src" {
    try doTheTest();
}

fn doTheTest() !void {
    const src = @src();

    try expect(src.line == 9);
    try expect(src.column == 17);
    try expect(std.mem.endsWith(u8, src.fn_name, "doTheTest"));
    try expect(std.mem.endsWith(u8, src.file, "test_src_builtin.zig"));
}

$ zig test test_src_builtin.zig
1/1 test_src_builtin.test.@src...OK
All 1 tests passed.

const std = @import("std");
const expect = std.testing.expect;

test "@This()" {
    var items = [_]i32{ 1, 2, 3, 4 };
    const list = List(i32){ .items = items[0..] };
    try expect(list.length() == 4);
}

fn List(comptime T: type) type {
    return struct {
        const Self = @This();

        items: []T,

        fn length(self: Self) usize {
            return self.items.len;
        }
    };
}

$ zig test test_this_builtin.zig
1/1 test_this_builtin.test.@This()...OK
All 1 tests passed.

const std = @import("std");
const expect = std.testing.expect;

test "integer truncation" {
    const a: u16 = 0xabcd;
    const b: u8 = @truncate(a);
    try expect(b == 0xcd);
}

$ zig test test_truncate_builtin.zig
1/1 test_truncate_builtin.test.integer truncation...OK
All 1 tests passed.

const std = @import("std");
const expect = std.testing.expect;

test "no runtime side effects" {
    var data: i32 = 0;
    const T = @TypeOf(foo(i32, &data));
    try comptime expect(T == i32);
    try expect(data == 0);
}

fn foo(comptime T: type, ptr: *T) T {
    ptr.* += 1;
    return ptr.*;
}

$ zig test test_TypeOf_builtin.zig
1/1 test_TypeOf_builtin.test.no runtime side effects...OK
All 1 tests passed.

const std = @import("std");

pub fn build(b: *std.Build) void {
    const optimize = b.standardOptimizeOption(.{});
    const exe = b.addExecutable(.{
        .name = "example",
        .root_source_file = b.path("example.zig"),
        .optimize = optimize,
    });
    b.default_step.dependOn(&exe.step);
}

$ zig build-exe example.zig

$ zig build-exe example.zig -O ReleaseFast

$ zig build-exe example.zig -O ReleaseSafe

$ zig build-exe example.zig -O ReleaseSmall

test "safety check" {
    unreachable;
}

$ zig test test_undefined_behavior.zig
1/1 test_undefined_behavior.test.safety check...thread 3571226 panic: reached unreachable code
/home/andy/src/zig/doc/langref/test_undefined_behavior.zig:2:5: 0x103ce30 in test.safety check (test)
    unreachable;
    ^
/home/andy/src/zig/lib/compiler/test_runner.zig:157:25: 0x1048260 in mainTerminal (test)
        if (test_fn.func()) |_| {
                        ^
/home/andy/src/zig/lib/compiler/test_runner.zig:37:28: 0x103e21b in main (test)
        return mainTerminal();
                           ^
/home/andy/src/zig/lib/std/start.zig:514:22: 0x103d359 in posixCallMainAndExit (test)
            root.main();
                     ^
/home/andy/src/zig/lib/std/start.zig:266:5: 0x103cec1 in _start (test)
    asm volatile (switch (native_arch) {
    ^
???:?:?: 0x0 in ??? (???)
error: the following test command crashed:
/home/andy/src/zig/.zig-cache/o/a71f9f37afd5b3c603d2b9ea72373fa7/test

comptime {
    assert(false);
}
fn assert(ok: bool) void {
    if (!ok) unreachable; // assertion failure
}

$ zig test test_comptime_reaching_unreachable.zig
doc/langref/test_comptime_reaching_unreachable.zig:5:14: error: reached unreachable code
    if (!ok) unreachable; // assertion failure
             ^~~~~~~~~~~
doc/langref/test_comptime_reaching_unreachable.zig:2:11: note: called from here
    assert(false);
    ~~~~~~^~~~~~~

const std = @import("std");

pub fn main() void {
    std.debug.assert(false);
}

$ zig build-exe runtime_reaching_unreachable.zig
$ ./runtime_reaching_unreachable
thread 3575642 panic: reached unreachable code
/home/andy/src/zig/lib/std/debug.zig:412:14: 0x1036cdd in assert (runtime_reaching_unreachable)
    if (!ok) unreachable; // assertion failure
             ^
/home/andy/src/zig/doc/langref/runtime_reaching_unreachable.zig:4:21: 0x103507a in main (runtime_reaching_unreachable)
    std.debug.assert(false);
                    ^
/home/andy/src/zig/lib/std/start.zig:514:22: 0x1034929 in posixCallMainAndExit (runtime_reaching_unreachable)
            root.main();
                     ^
/home/andy/src/zig/lib/std/start.zig:266:5: 0x1034491 in _start (runtime_reaching_unreachable)
    asm volatile (switch (native_arch) {
    ^
???:?:?: 0x0 in ??? (???)
(process terminated by signal)

comptime {
    const array: [5]u8 = "hello".*;
    const garbage = array[5];
    _ = garbage;
}

$ zig test test_comptime_index_out_of_bounds.zig
doc/langref/test_comptime_index_out_of_bounds.zig:3:27: error: index 5 outside array of length 5
    const garbage = array[5];
                          ^

pub fn main() void {
    const x = foo("hello");
    _ = x;
}

fn foo(x: []const u8) u8 {
    return x[5];
}

$ zig build-exe runtime_index_out_of_bounds.zig
$ ./runtime_index_out_of_bounds
thread 3567952 panic: index out of bounds: index 5, len 5
/home/andy/src/zig/doc/langref/runtime_index_out_of_bounds.zig:7:13: 0x1037169 in foo (runtime_index_out_of_bounds)
    return x[5];
            ^
/home/andy/src/zig/doc/langref/runtime_index_out_of_bounds.zig:2:18: 0x10350b6 in main (runtime_index_out_of_bounds)
    const x = foo("hello");
                 ^
/home/andy/src/zig/lib/std/start.zig:514:22: 0x1034959 in posixCallMainAndExit (runtime_index_out_of_bounds)
            root.main();
                     ^
/home/andy/src/zig/lib/std/start.zig:266:5: 0x10344c1 in _start (runtime_index_out_of_bounds)
    asm volatile (switch (native_arch) {
    ^
???:?:?: 0x0 in ??? (???)
(process terminated by signal)

comptime {
    const value: i32 = -1;
    const unsigned: u32 = @intCast(value);
    _ = unsigned;
}

$ zig test test_comptime_invalid_cast.zig
doc/langref/test_comptime_invalid_cast.zig:3:36: error: type 'u32' cannot represent integer value '-1'
    const unsigned: u32 = @intCast(value);
                                   ^~~~~

const std = @import("std");

pub fn main() void {
    var value: i32 = -1; // runtime-known
    _ = &value;
    const unsigned: u32 = @intCast(value);
    std.debug.print("value: {}\n", .{unsigned});
}

$ zig build-exe runtime_invalid_cast.zig
$ ./runtime_invalid_cast
thread 3567914 panic: attempt to cast negative value to unsigned integer
/home/andy/src/zig/doc/langref/runtime_invalid_cast.zig:6:27: 0x10351e2 in main (runtime_invalid_cast)
    const unsigned: u32 = @intCast(value);
                          ^
/home/andy/src/zig/lib/std/start.zig:514:22: 0x1034a49 in posixCallMainAndExit (runtime_invalid_cast)
            root.main();
                     ^
/home/andy/src/zig/lib/std/start.zig:266:5: 0x10345b1 in _start (runtime_invalid_cast)
    asm volatile (switch (native_arch) {
    ^
???:?:?: 0x0 in ??? (???)
(process terminated by signal)

comptime {
    const spartan_count: u16 = 300;
    const byte: u8 = @intCast(spartan_count);
    _ = byte;
}

$ zig test test_comptime_invalid_cast_truncate.zig
doc/langref/test_comptime_invalid_cast_truncate.zig:3:31: error: type 'u8' cannot represent integer value '300'
    const byte: u8 = @intCast(spartan_count);
                              ^~~~~~~~~~~~~

const std = @import("std");

pub fn main() void {
    var spartan_count: u16 = 300; // runtime-known
    _ = &spartan_count;
    const byte: u8 = @intCast(spartan_count);
    std.debug.print("value: {}\n", .{byte});
}

$ zig build-exe runtime_invalid_cast_truncate.zig
$ ./runtime_invalid_cast_truncate
thread 3576020 panic: integer cast truncated bits
/home/andy/src/zig/doc/langref/runtime_invalid_cast_truncate.zig:6:22: 0x1035275 in main (runtime_invalid_cast_truncate)
    const byte: u8 = @intCast(spartan_count);
                     ^
/home/andy/src/zig/lib/std/start.zig:514:22: 0x1034ad9 in posixCallMainAndExit (runtime_invalid_cast_truncate)
            root.main();
                     ^
/home/andy/src/zig/lib/std/start.zig:266:5: 0x1034641 in _start (runtime_invalid_cast_truncate)
    asm volatile (switch (native_arch) {
    ^
???:?:?: 0x0 in ??? (???)
(process terminated by signal)

comptime {
    var byte: u8 = 255;
    byte += 1;
}

$ zig test test_comptime_overflow.zig
doc/langref/test_comptime_overflow.zig:3:10: error: overflow of integer type 'u8' with value '256'
    byte += 1;
    ~~~~~^~~~

const std = @import("std");

pub fn main() void {
    var byte: u8 = 255;
    byte += 1;
    std.debug.print("value: {}\n", .{byte});
}

$ zig build-exe runtime_overflow.zig
$ ./runtime_overflow
thread 3574209 panic: integer overflow
/home/andy/src/zig/doc/langref/runtime_overflow.zig:5:10: 0x103525e in main (runtime_overflow)
    byte += 1;
         ^
/home/andy/src/zig/lib/std/start.zig:514:22: 0x1034ad9 in posixCallMainAndExit (runtime_overflow)
            root.main();
                     ^
/home/andy/src/zig/lib/std/start.zig:266:5: 0x1034641 in _start (runtime_overflow)
    asm volatile (switch (native_arch) {
    ^
???:?:?: 0x0 in ??? (???)
(process terminated by signal)

const math = @import("std").math;
const print = @import("std").debug.print;
pub fn main() !void {
    var byte: u8 = 255;

    byte = if (math.add(u8, byte, 1)) |result| result else |err| {
        print("unable to add one: {s}\n", .{@errorName(err)});
        return err;
    };

    print("result: {}\n", .{byte});
}

$ zig build-exe math_add.zig
$ ./math_add
unable to add one: Overflow
error: Overflow
/home/andy/src/zig/lib/std/math.zig:565:21: 0x10352a5 in add__anon_2592 (math_add)
    if (ov[1] != 0) return error.Overflow;
                    ^
/home/andy/src/zig/doc/langref/math_add.zig:8:9: 0x1035243 in main (math_add)
        return err;
        ^

const print = @import("std").debug.print;
pub fn main() void {
    const byte: u8 = 255;

    const ov = @addWithOverflow(byte, 10);
    if (ov[1] != 0) {
        print("overflowed result: {}\n", .{ov[0]});
    } else {
        print("result: {}\n", .{ov[0]});
    }
}

$ zig build-exe addWithOverflow_builtin.zig
$ ./addWithOverflow_builtin
overflowed result: 9

const std = @import("std");
const expect = std.testing.expect;
const minInt = std.math.minInt;
const maxInt = std.math.maxInt;

test "wraparound addition and subtraction" {
    const x: i32 = maxInt(i32);
    const min_val = x +% 1;
    try expect(min_val == minInt(i32));
    const max_val = min_val -% 1;
    try expect(max_val == maxInt(i32));
}

$ zig test test_wraparound_semantics.zig
1/1 test_wraparound_semantics.test.wraparound addition and subtraction...OK
All 1 tests passed.

comptime {
    const x = @shlExact(@as(u8, 0b01010101), 2);
    _ = x;
}

$ zig test test_comptime_shlExact_overwlow.zig
doc/langref/test_comptime_shlExact_overwlow.zig:2:15: error: operation caused overflow
    const x = @shlExact(@as(u8, 0b01010101), 2);
              ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

const std = @import("std");

pub fn main() void {
    var x: u8 = 0b01010101; // runtime-known
    _ = &x;
    const y = @shlExact(x, 2);
    std.debug.print("value: {}\n", .{y});
}

$ zig build-exe runtime_shlExact_overflow.zig
$ ./runtime_shlExact_overflow
thread 3577156 panic: left shift overflowed bits
/home/andy/src/zig/doc/langref/runtime_shlExact_overflow.zig:6:5: 0x10352bd in main (runtime_shlExact_overflow)
    const y = @shlExact(x, 2);
    ^
/home/andy/src/zig/lib/std/start.zig:514:22: 0x1034b19 in posixCallMainAndExit (runtime_shlExact_overflow)
            root.main();
                     ^
/home/andy/src/zig/lib/std/start.zig:266:5: 0x1034681 in _start (runtime_shlExact_overflow)
    asm volatile (switch (native_arch) {
    ^
???:?:?: 0x0 in ??? (???)
(process terminated by signal)

comptime {
    const x = @shrExact(@as(u8, 0b10101010), 2);
    _ = x;
}

$ zig test test_comptime_shrExact_overflow.zig
doc/langref/test_comptime_shrExact_overflow.zig:2:15: error: exact shift shifted out 1 bits
    const x = @shrExact(@as(u8, 0b10101010), 2);
              ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

const std = @import("std");

pub fn main() void {
    var x: u8 = 0b10101010; // runtime-known
    _ = &x;
    const y = @shrExact(x, 2);
    std.debug.print("value: {}\n", .{y});
}

$ zig build-exe runtime_shrExact_overflow.zig
$ ./runtime_shrExact_overflow
thread 3579049 panic: right shift overflowed bits
/home/andy/src/zig/doc/langref/runtime_shrExact_overflow.zig:6:5: 0x10352b9 in main (runtime_shrExact_overflow)
    const y = @shrExact(x, 2);
    ^
/home/andy/src/zig/lib/std/start.zig:514:22: 0x1034b19 in posixCallMainAndExit (runtime_shrExact_overflow)
            root.main();
                     ^
/home/andy/src/zig/lib/std/start.zig:266:5: 0x1034681 in _start (runtime_shrExact_overflow)
    asm volatile (switch (native_arch) {
    ^
???:?:?: 0x0 in ??? (???)
(process terminated by signal)

comptime {
    const a: i32 = 1;
    const b: i32 = 0;
    const c = a / b;
    _ = c;
}

$ zig test test_comptime_division_by_zero.zig
doc/langref/test_comptime_division_by_zero.zig:4:19: error: division by zero here causes undefined behavior
    const c = a / b;
                  ^

const std = @import("std");

pub fn main() void {
    var a: u32 = 1;
    var b: u32 = 0;
    _ = .{ &a, &b };
    const c = a / b;
    std.debug.print("value: {}\n", .{c});
}

$ zig build-exe runtime_division_by_zero.zig
$ ./runtime_division_by_zero
thread 3575479 panic: division by zero
/home/andy/src/zig/doc/langref/runtime_division_by_zero.zig:7:17: 0x10351f6 in main (runtime_division_by_zero)
    const c = a / b;
                ^
/home/andy/src/zig/lib/std/start.zig:514:22: 0x1034a49 in posixCallMainAndExit (runtime_division_by_zero)
            root.main();
                     ^
/home/andy/src/zig/lib/std/start.zig:266:5: 0x10345b1 in _start (runtime_division_by_zero)
    asm volatile (switch (native_arch) {
    ^
???:?:?: 0x0 in ??? (???)
(process terminated by signal)

comptime {
    const a: i32 = 10;
    const b: i32 = 0;
    const c = a % b;
    _ = c;
}

$ zig test test_comptime_remainder_division_by_zero.zig
doc/langref/test_comptime_remainder_division_by_zero.zig:4:19: error: division by zero here causes undefined behavior
    const c = a % b;
                  ^

const std = @import("std");

pub fn main() void {
    var a: u32 = 10;
    var b: u32 = 0;
    _ = .{ &a, &b };
    const c = a % b;
    std.debug.print("value: {}\n", .{c});
}

$ zig build-exe runtime_remainder_division_by_zero.zig
$ ./runtime_remainder_division_by_zero
thread 3570535 panic: division by zero
/home/andy/src/zig/doc/langref/runtime_remainder_division_by_zero.zig:7:17: 0x10351f6 in main (runtime_remainder_division_by_zero)
    const c = a % b;
                ^
/home/andy/src/zig/lib/std/start.zig:514:22: 0x1034a49 in posixCallMainAndExit (runtime_remainder_division_by_zero)
            root.main();
                     ^
/home/andy/src/zig/lib/std/start.zig:266:5: 0x10345b1 in _start (runtime_remainder_division_by_zero)
    asm volatile (switch (native_arch) {
    ^
???:?:?: 0x0 in ??? (???)
(process terminated by signal)

comptime {
    const a: u32 = 10;
    const b: u32 = 3;
    const c = @divExact(a, b);
    _ = c;
}

$ zig test test_comptime_divExact_remainder.zig
doc/langref/test_comptime_divExact_remainder.zig:4:15: error: exact division produced remainder
    const c = @divExact(a, b);
              ^~~~~~~~~~~~~~~

const std = @import("std");

pub fn main() void {
    var a: u32 = 10;
    var b: u32 = 3;
    _ = .{ &a, &b };
    const c = @divExact(a, b);
    std.debug.print("value: {}\n", .{c});
}

$ zig build-exe runtime_divExact_remainder.zig
$ ./runtime_divExact_remainder
thread 3570103 panic: exact division produced remainder
/home/andy/src/zig/doc/langref/runtime_divExact_remainder.zig:7:15: 0x103526b in main (runtime_divExact_remainder)
    const c = @divExact(a, b);
              ^
/home/andy/src/zig/lib/std/start.zig:514:22: 0x1034a89 in posixCallMainAndExit (runtime_divExact_remainder)
            root.main();
                     ^
/home/andy/src/zig/lib/std/start.zig:266:5: 0x10345f1 in _start (runtime_divExact_remainder)
    asm volatile (switch (native_arch) {
    ^
???:?:?: 0x0 in ??? (???)
(process terminated by signal)

comptime {
    const optional_number: ?i32 = null;
    const number = optional_number.?;
    _ = number;
}

$ zig test test_comptime_unwrap_null.zig
doc/langref/test_comptime_unwrap_null.zig:3:35: error: unable to unwrap null
    const number = optional_number.?;
                   ~~~~~~~~~~~~~~~^~

const std = @import("std");

pub fn main() void {
    var optional_number: ?i32 = null;
    _ = &optional_number;
    const number = optional_number.?;
    std.debug.print("value: {}\n", .{number});
}

$ zig build-exe runtime_unwrap_null.zig
$ ./runtime_unwrap_null
thread 3570514 panic: attempt to use null value
/home/andy/src/zig/doc/langref/runtime_unwrap_null.zig:6:35: 0x1035272 in main (runtime_unwrap_null)
    const number = optional_number.?;
                                  ^
/home/andy/src/zig/lib/std/start.zig:514:22: 0x1034ad9 in posixCallMainAndExit (runtime_unwrap_null)
            root.main();
                     ^
/home/andy/src/zig/lib/std/start.zig:266:5: 0x1034641 in _start (runtime_unwrap_null)
    asm volatile (switch (native_arch) {
    ^
???:?:?: 0x0 in ??? (???)
(process terminated by signal)

const print = @import("std").debug.print;
pub fn main() void {
    const optional_number: ?i32 = null;

    if (optional_number) |number| {
        print("got number: {}\n", .{number});
    } else {
        print("it's null\n", .{});
    }
}

$ zig build-exe testing_null_with_if.zig
$ ./testing_null_with_if
it's null

comptime {
    const number = getNumberOrFail() catch unreachable;
    _ = number;
}

fn getNumberOrFail() !i32 {
    return error.UnableToReturnNumber;
}

$ zig test test_comptime_unwrap_error.zig
doc/langref/test_comptime_unwrap_error.zig:2:44: error: caught unexpected error 'UnableToReturnNumber'
    const number = getNumberOrFail() catch unreachable;
                                           ^~~~~~~~~~~
doc/langref/test_comptime_unwrap_error.zig:7:18: note: error returned here
    return error.UnableToReturnNumber;
                 ^~~~~~~~~~~~~~~~~~~~

const std = @import("std");

pub fn main() void {
    const number = getNumberOrFail() catch unreachable;
    std.debug.print("value: {}\n", .{number});
}

fn getNumberOrFail() !i32 {
    return error.UnableToReturnNumber;
}

$ zig build-exe runtime_unwrap_error.zig
$ ./runtime_unwrap_error
thread 3577877 panic: attempt to unwrap error: UnableToReturnNumber
/home/andy/src/zig/doc/langref/runtime_unwrap_error.zig:9:5: 0x103738f in getNumberOrFail (runtime_unwrap_error)
    return error.UnableToReturnNumber;
    ^
/home/andy/src/zig/doc/langref/runtime_unwrap_error.zig:4:44: 0x1035301 in main (runtime_unwrap_error)
    const number = getNumberOrFail() catch unreachable;
                                           ^
/home/andy/src/zig/lib/std/start.zig:514:22: 0x1034b49 in posixCallMainAndExit (runtime_unwrap_error)
            root.main();
                     ^
/home/andy/src/zig/lib/std/start.zig:266:5: 0x10346b1 in _start (runtime_unwrap_error)
    asm volatile (switch (native_arch) {
    ^
???:?:?: 0x0 in ??? (???)
(process terminated by signal)

const print = @import("std").debug.print;

pub fn main() void {
    const result = getNumberOrFail();

    if (result) |number| {
        print("got number: {}\n", .{number});
    } else |err| {
        print("got error: {s}\n", .{@errorName(err)});
    }
}

fn getNumberOrFail() !i32 {
    return error.UnableToReturnNumber;
}

$ zig build-exe testing_error_with_if.zig
$ ./testing_error_with_if
got error: UnableToReturnNumber

comptime {
    const err = error.AnError;
    const number = @intFromError(err) + 10;
    const invalid_err = @errorFromInt(number);
    _ = invalid_err;
}

$ zig test test_comptime_invalid_error_code.zig
doc/langref/test_comptime_invalid_error_code.zig:4:39: error: integer value '11' represents no error
    const invalid_err = @errorFromInt(number);
                                      ^~~~~~

const std = @import("std");

pub fn main() void {
    const err = error.AnError;
    var number = @intFromError(err) + 500;
    _ = &number;
    const invalid_err = @errorFromInt(number);
    std.debug.print("value: {}\n", .{invalid_err});
}

$ zig build-exe runtime_invalid_error_code.zig
$ ./runtime_invalid_error_code
thread 3570441 panic: invalid error code
/home/andy/src/zig/doc/langref/runtime_invalid_error_code.zig:7:5: 0x10352a0 in main (runtime_invalid_error_code)
    const invalid_err = @errorFromInt(number);
    ^
/home/andy/src/zig/lib/std/start.zig:514:22: 0x1034ae9 in posixCallMainAndExit (runtime_invalid_error_code)
            root.main();
                     ^
/home/andy/src/zig/lib/std/start.zig:266:5: 0x1034651 in _start (runtime_invalid_error_code)
    asm volatile (switch (native_arch) {
    ^
???:?:?: 0x0 in ??? (???)
(process terminated by signal)

const Foo = enum {
    a,
    b,
    c,
};
comptime {
    const a: u2 = 3;
    const b: Foo = @enumFromInt(a);
    _ = b;
}

$ zig test test_comptime_invalid_enum_cast.zig
doc/langref/test_comptime_invalid_enum_cast.zig:8:20: error: enum 'test_comptime_invalid_enum_cast.Foo' has no tag with value '3'
    const b: Foo = @enumFromInt(a);
                   ^~~~~~~~~~~~~~~
doc/langref/test_comptime_invalid_enum_cast.zig:1:13: note: enum declared here
const Foo = enum {
            ^~~~

const std = @import("std");

const Foo = enum {
    a,
    b,
    c,
};

pub fn main() void {
    var a: u2 = 3;
    _ = &a;
    const b: Foo = @enumFromInt(a);
    std.debug.print("value: {s}\n", .{@tagName(b)});
}

$ zig build-exe runtime_invalid_enum_cast.zig
$ ./runtime_invalid_enum_cast
thread 3568027 panic: invalid enum value
/home/andy/src/zig/doc/langref/runtime_invalid_enum_cast.zig:12:20: 0x1035297 in main (runtime_invalid_enum_cast)
    const b: Foo = @enumFromInt(a);
                   ^
/home/andy/src/zig/lib/std/start.zig:514:22: 0x1034af9 in posixCallMainAndExit (runtime_invalid_enum_cast)
            root.main();
                     ^
/home/andy/src/zig/lib/std/start.zig:266:5: 0x1034661 in _start (runtime_invalid_enum_cast)
    asm volatile (switch (native_arch) {
    ^
???:?:?: 0x0 in ??? (???)
(process terminated by signal)

const Set1 = error{
    A,
    B,
};
const Set2 = error{
    A,
    C,
};
comptime {
    _ = @as(Set2, @errorCast(Set1.B));
}

$ zig test test_comptime_invalid_error_set_cast.zig
doc/langref/test_comptime_invalid_error_set_cast.zig:10:19: error: 'error.B' not a member of error set 'error{A,C}'
    _ = @as(Set2, @errorCast(Set1.B));
                  ^~~~~~~~~~~~~~~~~~

const std = @import("std");

const Set1 = error{
    A,
    B,
};
const Set2 = error{
    A,
    C,
};
pub fn main() void {
    foo(Set1.B);
}
fn foo(set1: Set1) void {
    const x: Set2 = @errorCast(set1);
    std.debug.print("value: {}\n", .{x});
}

$ zig build-exe runtime_invalid_error_set_cast.zig
$ ./runtime_invalid_error_set_cast
thread 3568026 panic: invalid error code
/home/andy/src/zig/doc/langref/runtime_invalid_error_set_cast.zig:15:21: 0x1037317 in foo (runtime_invalid_error_set_cast)
    const x: Set2 = @errorCast(set1);
                    ^
/home/andy/src/zig/doc/langref/runtime_invalid_error_set_cast.zig:12:8: 0x103523d in main (runtime_invalid_error_set_cast)
    foo(Set1.B);
       ^
/home/andy/src/zig/lib/std/start.zig:514:22: 0x1034ae9 in posixCallMainAndExit (runtime_invalid_error_set_cast)
            root.main();
                     ^
/home/andy/src/zig/lib/std/start.zig:266:5: 0x1034651 in _start (runtime_invalid_error_set_cast)
    asm volatile (switch (native_arch) {
    ^
???:?:?: 0x0 in ??? (???)
(process terminated by signal)

comptime {
    const ptr: *align(1) i32 = @ptrFromInt(0x1);
    const aligned: *align(4) i32 = @alignCast(ptr);
    _ = aligned;
}

$ zig test test_comptime_incorrect_pointer_alignment.zig
doc/langref/test_comptime_incorrect_pointer_alignment.zig:3:47: error: pointer address 0x1 is not aligned to 4 bytes
    const aligned: *align(4) i32 = @alignCast(ptr);
                                              ^~~

const mem = @import("std").mem;
pub fn main() !void {
    var array align(4) = [_]u32{ 0x11111111, 0x11111111 };
    const bytes = mem.sliceAsBytes(array[0..]);
    if (foo(bytes) != 0x11111111) return error.Wrong;
}
fn foo(bytes: []u8) u32 {
    const slice4 = bytes[1..5];
    const int_slice = mem.bytesAsSlice(u32, @as([]align(4) u8, @alignCast(slice4)));
    return int_slice[0];
}

$ zig build-exe runtime_incorrect_pointer_alignment.zig
$ ./runtime_incorrect_pointer_alignment
thread 3570122 panic: incorrect alignment
/home/andy/src/zig/doc/langref/runtime_incorrect_pointer_alignment.zig:9:64: 0x1034f0a in foo (runtime_incorrect_pointer_alignment)
    const int_slice = mem.bytesAsSlice(u32, @as([]align(4) u8, @alignCast(slice4)));
                                                               ^
/home/andy/src/zig/doc/langref/runtime_incorrect_pointer_alignment.zig:5:12: 0x1034dc7 in main (runtime_incorrect_pointer_alignment)
    if (foo(bytes) != 0x11111111) return error.Wrong;
           ^
/home/andy/src/zig/lib/std/start.zig:524:37: 0x1034cc5 in posixCallMainAndExit (runtime_incorrect_pointer_alignment)
            const result = root.main() catch |err| {
                                    ^
/home/andy/src/zig/lib/std/start.zig:266:5: 0x10347e1 in _start (runtime_incorrect_pointer_alignment)
    asm volatile (switch (native_arch) {
    ^
???:?:?: 0x0 in ??? (???)
(process terminated by signal)

comptime {
    var f = Foo{ .int = 42 };
    f.float = 12.34;
}

const Foo = union {
    float: f32,
    int: u32,
};

$ zig test test_comptime_wrong_union_field_access.zig
doc/langref/test_comptime_wrong_union_field_access.zig:3:6: error: access of union field 'float' while field 'int' is active
    f.float = 12.34;
    ~^~~~~~
doc/langref/test_comptime_wrong_union_field_access.zig:6:13: note: union declared here
const Foo = union {
            ^~~~~

const std = @import("std");

const Foo = union {
    float: f32,
    int: u32,
};

pub fn main() void {
    var f = Foo{ .int = 42 };
    bar(&f);
}

fn bar(f: *Foo) void {
    f.float = 12.34;
    std.debug.print("value: {}\n", .{f.float});
}

$ zig build-exe runtime_wrong_union_field_access.zig
$ ./runtime_wrong_union_field_access
thread 3578787 panic: access of union field 'float' while field 'int' is active
/home/andy/src/zig/doc/langref/runtime_wrong_union_field_access.zig:14:6: 0x103cd20 in bar (runtime_wrong_union_field_access)
    f.float = 12.34;
     ^
/home/andy/src/zig/doc/langref/runtime_wrong_union_field_access.zig:10:8: 0x103ac5c in main (runtime_wrong_union_field_access)
    bar(&f);
       ^
/home/andy/src/zig/lib/std/start.zig:514:22: 0x103a4f9 in posixCallMainAndExit (runtime_wrong_union_field_access)
            root.main();
                     ^
/home/andy/src/zig/lib/std/start.zig:266:5: 0x103a061 in _start (runtime_wrong_union_field_access)
    asm volatile (switch (native_arch) {
    ^
???:?:?: 0x0 in ??? (???)
(process terminated by signal)

const std = @import("std");

const Foo = union {
    float: f32,
    int: u32,
};

pub fn main() void {
    var f = Foo{ .int = 42 };
    bar(&f);
}

fn bar(f: *Foo) void {
    f.* = Foo{ .float = 12.34 };
    std.debug.print("value: {}\n", .{f.float});
}

$ zig build-exe change_active_union_field.zig
$ ./change_active_union_field
value: 1.234e1

const std = @import("std");

const Foo = union {
    float: f32,
    int: u32,
};

pub fn main() void {
    var f = Foo{ .int = 42 };
    f = Foo{ .float = undefined };
    bar(&f);
    std.debug.print("value: {}\n", .{f.float});
}

fn bar(f: *Foo) void {
    f.float = 12.34;
}

$ zig build-exe undefined_active_union_field.zig
$ ./undefined_active_union_field
value: 1.234e1

comptime {
    const float: f32 = 4294967296;
    const int: i32 = @intFromFloat(float);
    _ = int;
}

$ zig test test_comptime_out_of_bounds_float_to_integer_cast.zig
doc/langref/test_comptime_out_of_bounds_float_to_integer_cast.zig:3:36: error: float value '4294967296' cannot be stored in integer type 'i32'
    const int: i32 = @intFromFloat(float);
                                   ^~~~~

pub fn main() void {
    var float: f32 = 4294967296; // runtime-known
    _ = &float;
    const int: i32 = @intFromFloat(float);
    _ = int;
}

$ zig build-exe runtime_out_of_bounds_float_to_integer_cast.zig
$ ./runtime_out_of_bounds_float_to_integer_cast
thread 3570320 panic: integer part of floating point value out of bounds
/home/andy/src/zig/doc/langref/runtime_out_of_bounds_float_to_integer_cast.zig:4:22: 0x1035169 in main (runtime_out_of_bounds_float_to_integer_cast)
    const int: i32 = @intFromFloat(float);
                     ^
/home/andy/src/zig/lib/std/start.zig:514:22: 0x10349a9 in posixCallMainAndExit (runtime_out_of_bounds_float_to_integer_cast)
            root.main();
                     ^
/home/andy/src/zig/lib/std/start.zig:266:5: 0x1034511 in _start (runtime_out_of_bounds_float_to_integer_cast)
    asm volatile (switch (native_arch) {
    ^
???:?:?: 0x0 in ??? (???)
(process terminated by signal)

comptime {
    const opt_ptr: ?*i32 = null;
    const ptr: *i32 = @ptrCast(opt_ptr);
    _ = ptr;
}

$ zig test test_comptime_invalid_null_pointer_cast.zig
doc/langref/test_comptime_invalid_null_pointer_cast.zig:3:32: error: null pointer casted to type '*i32'
    const ptr: *i32 = @ptrCast(opt_ptr);
                               ^~~~~~~

pub fn main() void {
    var opt_ptr: ?*i32 = null;
    _ = &opt_ptr;
    const ptr: *i32 = @ptrCast(opt_ptr);
    _ = ptr;
}

$ zig build-exe runtime_invalid_null_pointer_cast.zig
$ ./runtime_invalid_null_pointer_cast
thread 3572791 panic: cast causes pointer to be null
/home/andy/src/zig/doc/langref/runtime_invalid_null_pointer_cast.zig:4:23: 0x10350bc in main (runtime_invalid_null_pointer_cast)
    const ptr: *i32 = @ptrCast(opt_ptr);
                      ^
/home/andy/src/zig/lib/std/start.zig:514:22: 0x1034929 in posixCallMainAndExit (runtime_invalid_null_pointer_cast)
            root.main();
                     ^
/home/andy/src/zig/lib/std/start.zig:266:5: 0x1034491 in _start (runtime_invalid_null_pointer_cast)
    asm volatile (switch (native_arch) {
    ^
???:?:?: 0x0 in ??? (???)
(process terminated by signal)

const std = @import("std");
const Allocator = std.mem.Allocator;
const expect = std.testing.expect;

test "using an allocator" {
    var buffer: [100]u8 = undefined;
    var fba = std.heap.FixedBufferAllocator.init(&buffer);
    const allocator = fba.allocator();
    const result = try concat(allocator, "foo", "bar");
    try expect(std.mem.eql(u8, "foobar", result));
}

fn concat(allocator: Allocator, a: []const u8, b: []const u8) ![]u8 {
    const result = try allocator.alloc(u8, a.len + b.len);
    @memcpy(result[0..a.len], a);
    @memcpy(result[a.len..], b);
    return result;
}

$ zig test test_allocator.zig
1/1 test_allocator.test.using an allocator...OK
All 1 tests passed.

fn foo(s: []u8) void {
    _ = s;
}

test "string literal to mutable slice" {
    foo("hello");
}

$ zig test test_string_literal_to_slice.zig
doc/langref/test_string_literal_to_slice.zig:6:9: error: expected type '[]u8', found '*const [5:0]u8'
    foo("hello");
        ^~~~~~~
doc/langref/test_string_literal_to_slice.zig:6:9: note: cast discards const qualifier
doc/langref/test_string_literal_to_slice.zig:1:11: note: parameter type declared here
fn foo(s: []u8) void {
          ^~~~

fn foo(s: []const u8) void {
    _ = s;
}

test "string literal to constant slice" {
    foo("hello");
}

$ zig test test_string_literal_to_const_slice.zig
1/1 test_string_literal_to_const_slice.test.string literal to constant slice...OK
All 1 tests passed.

const builtin = @import("builtin");
const separator = if (builtin.os.tag == .windows) '\\' else '/';

const std = @import("std");
/// Zig version. When writing code that supports multiple versions of Zig, prefer
/// feature detection (i.e. with `@hasDecl` or `@hasField`) over version checks.
pub const zig_version = std.SemanticVersion.parse(zig_version_string) catch unreachable;
pub const zig_version_string = "0.13.0";
pub const zig_backend = std.builtin.CompilerBackend.stage2_llvm;

pub const output_mode = std.builtin.OutputMode.Exe;
pub const link_mode = std.builtin.LinkMode.static;
pub const is_test = false;
pub const single_threaded = false;
pub const abi = std.Target.Abi.gnu;
pub const cpu: std.Target.Cpu = .{
    .arch = .x86_64,
    .model = &std.Target.x86.cpu.znver4,
    .features = std.Target.x86.featureSet(&[_]std.Target.x86.Feature{
        .@"64bit",
        .adx,
        .aes,
        .allow_light_256_bit,
        .avx,
        .avx2,
        .avx512bf16,
        .avx512bitalg,
        .avx512bw,
        .avx512cd,
        .avx512dq,
        .avx512f,
        .avx512ifma,
        .avx512vbmi,
        .avx512vbmi2,
        .avx512vl,
        .avx512vnni,
        .avx512vpopcntdq,
        .bmi,
        .bmi2,
        .branchfusion,
        .clflushopt,
        .clwb,
        .clzero,
        .cmov,
        .crc32,
        .cx16,
        .cx8,
        .evex512,
        .f16c,
        .fast_15bytenop,
        .fast_bextr,
        .fast_lzcnt,
        .fast_movbe,
        .fast_scalar_fsqrt,
        .fast_scalar_shift_masks,
        .fast_variable_perlane_shuffle,
        .fast_vector_fsqrt,
        .fma,
        .fsgsbase,
        .fsrm,
        .fxsr,
        .gfni,
        .invpcid,
        .lzcnt,
        .macrofusion,
        .mmx,
        .movbe,
        .mwaitx,
        .nopl,
        .pclmul,
        .pku,
        .popcnt,
        .prfchw,
        .rdpid,
        .rdpru,
        .rdrnd,
        .rdseed,
        .sahf,
        .sbb_dep_breaking,
        .sha,
        .shstk,
        .slow_shld,
        .sse,
        .sse2,
        .sse3,
        .sse4_1,
        .sse4_2,
        .sse4a,
        .ssse3,
        .vaes,
        .vpclmulqdq,
        .vzeroupper,
        .wbnoinvd,
        .x87,
        .xsave,
        .xsavec,
        .xsaveopt,
        .xsaves,
    }),
};
pub const os = std.Target.Os{
    .tag = .linux,
    .version_range = .{ .linux = .{
        .range = .{
            .min = .{
                .major = 6,
                .minor = 9,
                .patch = 2,
            },
            .max = .{
                .major = 6,
                .minor = 9,
                .patch = 2,
            },
        },
        .glibc = .{
            .major = 2,
            .minor = 39,
            .patch = 0,
        },
    }},
};
pub const target: std.Target = .{
    .cpu = cpu,
    .os = os,
    .abi = abi,
    .ofmt = object_format,
    .dynamic_linker = std.Target.DynamicLinker.init("/nix/store/k7zgvzp2r31zkg9xqgjim7mbknryv6bs-glibc-2.39-52/lib/ld-linux-x86-64.so.2"),
};
pub const object_format = std.Target.ObjectFormat.elf;
pub const mode = std.builtin.OptimizeMode.Debug;
pub const link_libc = false;
pub const link_libcpp = false;
pub const have_error_return_tracing = true;
pub const valgrind_support = true;
pub const sanitize_thread = false;
pub const position_independent_code = false;
pub const position_independent_executable = false;
pub const strip_debug_info = false;
pub const code_model = std.builtin.CodeModel.default;
pub const omit_frame_pointer = false;

const c = @cImport({
    // See https://github.com/ziglang/zig/issues/515
    @cDefine("_NO_CRT_STDIO_INLINE", "1");
    @cInclude("stdio.h");
});
pub fn main() void {
    _ = c.printf("hello\n");
}

$ zig build-exe cImport_builtin.zig -lc
$ ./cImport_builtin
hello

const builtin = @import("builtin");

const c = @cImport({
    @cDefine("NDEBUG", builtin.mode == .ReleaseFast);
    if (something) {
        @cDefine("_GNU_SOURCE", {});
    }
    @cInclude("stdlib.h");
    if (something) {
        @cUndef("_GNU_SOURCE");
    }
    @cInclude("soundio.h");
});

long FOO = __LONG_MAX__;

$ zig translate-c -target thumb-freestanding-gnueabihf varytarget.h|grep FOO
pub export var FOO: c_long = 2147483647;
$ zig translate-c -target x86_64-macos-gnu varytarget.h|grep FOO
pub export var FOO: c_long = 9223372036854775807;

enum FOO { BAR };
int do_something(enum FOO foo);

$ zig translate-c varycflags.h|grep -B1 do_something
pub const enum_FOO = c_uint;
pub extern fn do_something(foo: enum_FOO) c_int;
$ zig translate-c -cflags -fshort-enums -- varycflags.h|grep -B1 do_something
pub const enum_FOO = u8;
pub extern fn do_something(foo: enum_FOO) c_int;

const c = @cImport({
    @cDefine("_NO_CRT_STDIO_INLINE", "1");
    @cInclude("stdio.h");
});
pub fn main() void {
    _ = c;
}

$ zig build-exe verbose_cimport_flag.zig -lc --verbose-cimport
info(compilation): C import source: /home/andy/src/zig/.zig-cache/o/f4e9c68cba40c97888f064d67b031021/cimport.h
info(compilation): C import .d file: /home/andy/src/zig/.zig-cache/o/f4e9c68cba40c97888f064d67b031021/cimport.h.d
info(compilation): C import output: /home/andy/src/zig/.zig-cache/o/1b63455e1d0d323f51bdc4909717e28b/cimport.zig
$ ./verbose_cimport_flag

#define MAKELOCAL(NAME, INIT) int NAME = INIT
int foo(void) {
   MAKELOCAL(a, 1);
   MAKELOCAL(b, 2);
   return a + b;
}

$ zig translate-c macro.c > macro.zig

pub export fn foo() c_int {
    var a: c_int = 1;
    _ = &a;
    var b: c_int = 2;
    _ = &b;
    return a + b;
}
pub const MAKELOCAL = @compileError("unable to translate C expr: unexpected token .Equal"); // macro.c:1:9

const std = @import("std");
const testing = std.testing;

pub extern "c" fn printf(format: [*:0]const u8, ...) c_int;

test "variadic function" {
    try testing.expect(printf("Hello, world!\n") == 14);
    try testing.expect(@typeInfo(@TypeOf(printf)).Fn.is_var_args);
}

$ zig test test_variadic_function.zig -lc
1/1 test_variadic_function.test.variadic function...OK
All 1 tests passed.
Hello, world!

const std = @import("std");
const testing = std.testing;
const builtin = @import("builtin");

fn add(count: c_int, ...) callconv(.C) c_int {
    var ap = @cVaStart();
    defer @cVaEnd(&ap);
    var i: usize = 0;
    var sum: c_int = 0;
    while (i < count) : (i += 1) {
        sum += @cVaArg(&ap, c_int);
    }
    return sum;
}

test "defining a variadic function" {
    if (builtin.cpu.arch == .aarch64 and builtin.os.tag != .macos) {
        // https://github.com/ziglang/zig/issues/14096
        return error.SkipZigTest;
    }
    if (builtin.cpu.arch == .x86_64 and builtin.os.tag == .windows) {
        // https://github.com/ziglang/zig/issues/16961
        return error.SkipZigTest;
    }

    try std.testing.expectEqual(@as(c_int, 0), add(0));
    try std.testing.expectEqual(@as(c_int, 1), add(1, @as(c_int, 1)));
    try std.testing.expectEqual(@as(c_int, 3), add(2, @as(c_int, 1), @as(c_int, 2)));
}

$ zig test test_defining_variadic_function.zig
1/1 test_defining_variadic_function.test.defining a variadic function...OK
All 1 tests passed.

export fn add(a: i32, b: i32) i32 {
    return a + b;
}

$ zig build-lib mathtest.zig

$ zig build-lib mathtest.zig -dynamic

// This header is generated by zig from mathtest.zig
#include "mathtest.h"
#include <stdio.h>

int main(int argc, char **argv) {
    int32_t result = add(42, 1337);
    printf("%d\n", result);
    return 0;
}

const std = @import("std");

pub fn build(b: *std.Build) void {
    const lib = b.addSharedLibrary(.{
        .name = "mathtest",
        .root_source_file = b.path("mathtest.zig"),
        .version = .{ .major = 1, .minor = 0, .patch = 0 },
    });
    const exe = b.addExecutable(.{
        .name = "test",
    });
    exe.addCSourceFile(.{ .file = b.path("test.c"), .flags = &.{"-std=c99"} });
    exe.linkLibrary(lib);
    exe.linkSystemLibrary("c");

    b.default_step.dependOn(&exe.step);

    const run_cmd = exe.run();

    const test_step = b.step("test", "Test the program");
    test_step.dependOn(&run_cmd.step);
}

$ zig build test
1379

const base64 = @import("std").base64;

export fn decode_base_64(
    dest_ptr: [*]u8,
    dest_len: usize,
    source_ptr: [*]const u8,
    source_len: usize,
) usize {
    const src = source_ptr[0..source_len];
    const dest = dest_ptr[0..dest_len];
    const base64_decoder = base64.standard.Decoder;
    const decoded_size = base64_decoder.calcSizeForSlice(src) catch unreachable;
    base64_decoder.decode(dest[0..decoded_size], src) catch unreachable;
    return decoded_size;
}

// This header is generated by zig from base64.zig
#include "base64.h"

#include <string.h>
#include <stdio.h>

int main(int argc, char **argv) {
    const char *encoded = "YWxsIHlvdXIgYmFzZSBhcmUgYmVsb25nIHRvIHVz";
    char buf[200];

    size_t len = decode_base_64(buf, 200, encoded, strlen(encoded));
    buf[len] = 0;
    puts(buf);

    return 0;
}

const std = @import("std");

pub fn build(b: *std.Build) void {
    const obj = b.addObject(.{
        .name = "base64",
        .root_source_file = b.path("base64.zig"),
    });

    const exe = b.addExecutable(.{
        .name = "test",
    });
    exe.addCSourceFile(.{ .file = b.path("test.c"), .flags = &.{"-std=c99"} });
    exe.addObject(obj);
    exe.linkSystemLibrary("c");
    b.installArtifact(exe);
}

$ zig build
$ ./zig-out/bin/test
all your base are belong to us

extern fn print(i32) void;

export fn add(a: i32, b: i32) void {
    print(a + b);
}

$ zig build-exe math.zig -target wasm32-freestanding -fno-entry --export=add

const fs = require('fs');
const source = fs.readFileSync("./math.wasm");
const typedArray = new Uint8Array(source);

WebAssembly.instantiate(typedArray, {
  env: {
    print: (result) => { console.log(`The result is ${result}`); }
  }}).then(result => {
  const add = result.instance.exports.add;
  add(1, 2);
});

$ node test.js
The result is 3

const std = @import("std");

pub fn main() !void {
    var general_purpose_allocator = std.heap.GeneralPurposeAllocator(.{}){};
    const gpa = general_purpose_allocator.allocator();
    const args = try std.process.argsAlloc(gpa);
    defer std.process.argsFree(gpa, args);

    for (args, 0..) |arg, i| {
        std.debug.print("{}: {s}\n", .{ i, arg });
    }
}

$ zig build-exe wasi_args.zig -target wasm32-wasi

$ wasmtime wasi_args.wasm 123 hello
0: wasi_args.wasm
1: 123
2: hello

const std = @import("std");
const fs = std.fs;

pub fn main() !void {
    var general_purpose_allocator = std.heap.GeneralPurposeAllocator(.{}){};
    const gpa = general_purpose_allocator.allocator();

    var arena_instance = std.heap.ArenaAllocator.init(gpa);
    defer arena_instance.deinit();
    const arena = arena_instance.allocator();

    const preopens = try fs.wasi.preopensAlloc(arena);

    for (preopens.names, 0..) |preopen, i| {
        std.debug.print("{}: {s}\n", .{ i, preopen });
    }
}

$ zig build-exe wasi_preopens.zig -target wasm32-wasi

$ wasmtime --dir=. wasi_preopens.wasm
0: stdin
1: stdout
2: stderr
3: .

const std = @import("std");

pub const json = struct {
    pub const JsonValue = union(enum) {
        number: f64,
        boolean: bool,
        // ...
    };
};

pub fn main() void {
    std.debug.print("{s}\n", .{@typeName(json.JsonValue)});
}

$ zig build-exe redundant_fqn.zig
$ ./redundant_fqn
redundant_fqn.json.JsonValue

const namespace_name = @import("dir_name/file_name.zig");
const TypeName = @import("dir_name/TypeName.zig");
var global_var: i32 = undefined;
const const_name = 42;
const primitive_type_alias = f32;
const string_alias = []u8;

const StructName = struct {
    field: i32,
};
const StructAlias = StructName;

fn functionName(param_name: TypeName) void {
    var functionPointer = functionName;
    functionPointer();
    functionPointer = otherFunction;
    functionPointer();
}
const functionAlias = functionName;

fn ListTemplateFunction(comptime ChildType: type, comptime fixed_size: usize) type {
    return List(ChildType, fixed_size);
}

fn ShortList(comptime T: type, comptime n: usize) type {
    return struct {
        field_name: [n]T,
        fn methodName() void {}
    };
}

// The word XML loses its casing when used in Zig identifiers.
const xml_document =
    \\<?xml version="1.0" encoding="UTF-8"?>
    \\<document>
    \\</document>
;
const XmlParser = struct {
    field: i32,
};

// The initials BE (Big Endian) are just another word in Zig identifier names.
fn readU32Be() u32 {}