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autobox(3)                           User Contributed Perl Documentation                          autobox(3)



NAME
       autobox - call methods on native types

SYNOPSIS
           use autobox;

           # integers

               my $range = 10->to(1); # [ 10, 9, 8, 7, 6, 5, 4, 3, 2, 1 ]

           # floats

               my $error = 3.1415927->minus(22/7)->abs();

           # strings

               my @list = 'SELECT * FROM foo'->list();
               my $greeting = "Hello, world!"->upper(); # "HELLO, WORLD!"

               $greeting->for_each(\&character_handler);

           # arrays and array refs

               my $schwartzian = @_->map(...)->sort(...)->map(...);
               my $hash = [ 'SELECT * FROM foo WHERE id IN (?, ?)', 1, 2 ]->hash();

           # hashes and hash refs

               { alpha => 'beta', gamma => 'vlissides' }->for_each(...);
               %hash->keys();

           # code refs

               my $plus_five = (\&add)->curry()->(5);
               my $minus_three = sub { $_[0] - $_[1] }->reverse->curry->(3);

           # can, isa, VERSION, import and unimport can be accessed via autobox_class

               42->autobox_class->isa('MyNumber')
               say []->autobox_class->VERSION

DESCRIPTION
       The autobox pragma allows methods to be called on integers, floats, strings, arrays, hashes, and code
       references in exactly the same manner as blessed references.

       The autoboxing is transparent: boxed values are not blessed into their (user-defined) implementation
       class (unless the method elects to bestow such a blessing) - they simply use its methods as though
       they are.

       The classes (packages) into which the native types are boxed are fully configurable.  By default, a
       method invoked on a non-object is assumed to be defined in a class whose name corresponds to the
       "ref()" type of that value - or SCALAR if the value is a non-reference.

       This mapping can be overridden by passing key/value pairs to the "use autobox" statement, in which
       the keys represent native types, and the values their associated classes.

       As with regular objects, autoboxed values are passed as the first argument of the specified method.
       Consequently, given a vanilla "use autobox":

           "Hello, world!"->upper()

       is invoked as:

           SCALAR::upper("hello, world!")

       while:

           [ 1 .. 10 ]->for_each(sub { ... })

       resolves to:

           ARRAY::for_each([ 1 .. 10 ], sub { ... })

       Values beginning with the array "@" and hash "%" sigils are passed by reference, i.e. under the
       default bindings:

           @array->join(', ')
           @{ ... }->length()
           %hash->keys()
           %$hash->values()

       are equivalent to:

           ARRAY::join(\@array, ', ')
           ARRAY::length(\@{ ... })
           HASH::keys(\%hash)
           HASH::values(\%$hash)

       Multiple "use autobox" statements can appear in the same scope. These are merged both "horizontally"
       (i.e.  multiple classes can be associated with a particular type) and "vertically" (i.e. multiple
       classes can be associated with multiple types).

       Thus:

           use autobox SCALAR => 'Foo';
           use autobox SCALAR => 'Bar';

       - associates SCALAR types with a synthetic class whose @ISA includes both "Foo" and "Bar" (in that
       order).

       Likewise:

           use autobox SCALAR => 'Foo';
           use autobox SCALAR => 'Bar';
           use autobox ARRAY  => 'Baz';

       and

           use autobox SCALAR => [ 'Foo', 'Bar' ];
           use autobox ARRAY  => 'Baz';

       - bind SCALAR types to the "Foo" and "Bar" classes and ARRAY types to "Baz".

       "autobox" is lexically scoped, and bindings for an outer scope can be extended or countermanded in a
       nested scope:

           {
               use autobox; # default bindings: autobox all native types
               ...

               {
                   # appends 'MyScalar' to the @ISA associated with SCALAR types
                   use autobox SCALAR => 'MyScalar';
                   ...
               }

               # back to the default (no MyScalar)
               ...
           }

       Autoboxing can be turned off entirely by using the "no" syntax:

           {
               use autobox;
               ...
               no autobox;
               ...
           }

       - or can be selectively disabled by passing arguments to the "no autobox" statement:

           use autobox; # default bindings

           no autobox qw(SCALAR);

           []->foo(); # OK: ARRAY::foo([])

           "Hello, world!"->bar(); # runtime error

       Autoboxing is not performed for barewords i.e.

           my $foo = Foo->new();

       and:

           my $foo = new Foo;

       behave as expected.

       Methods are called on native types by means of the arrow operator. As with regular objects, the right
       hand side of the operator can either be a bare method name or a variable containing a method name or
       subroutine reference. Thus the following are all valid:

           sub method1 { ... }
           my $method2 = 'some_method';
           my $method3 = sub { ... };
           my $method4 = \&some_method;

           " ... "->method1();
           [ ... ]->$method2();
           { ... }->$method3();
           sub { ... }->$method4();

       A native type is only asociated with a class if the type => class mapping is supplied in the "use
       autobox" statement. Thus the following will not work:

           use autobox SCALAR => 'MyScalar';

           @array->some_array_method();

       - as no class is specified for the ARRAY type. Note: the result of calling a method on a native type
       that is not associated with a class is the usual runtime error message:

           Can't call method "some_array_method" on unblessed reference at ...

       As a convenience, there is one exception to this rule. If "use autobox" is invoked with no arguments
       (ignoring the DEBUG option) the four main native types are associated with classes of the same name.

       Thus:

           use autobox;

       - is equivalent to:

           use autobox
               SCALAR => 'SCALAR',
               ARRAY  => 'ARRAY',
               HASH   => 'HASH',
               CODE   => 'CODE';

       This facilitates one-liners and prototypes:

           use autobox;

           sub SCALAR::split { [ split '', $_[0] ] }
           sub ARRAY::length { scalar @{$_[0]} }

           print "Hello, world!"->split->length();

       However, using these default bindings is not recommended as there's no guarantee that another piece
       of code won't trample over the same namespace/methods.

OPTIONS
       A mapping from native types to their user-defined classes can be specified by passing a list of
       key/value pairs to the "use autobox" statement.

       The following example shows the range of valid arguments:

           use autobox
               SCALAR    => 'MyScalar'                     # class name
               ARRAY     => 'MyNamespace::',               # class prefix (ending in '::')
               HASH      => [ 'MyHash', 'MyNamespace::' ], # one or more class names and/or prefixes
               CODE      => ...,                           # any of the 3 value types above
               INTEGER   => ...,                           # any of the 3 value types above
               FLOAT     => ...,                           # any of the 3 value types above
               NUMBER    => ...,                           # any of the 3 value types above
               STRING    => ...,                           # any of the 3 value types above
               UNDEF     => ...,                           # any of the 3 value types above
               UNIVERSAL => ...,                           # any of the 3 value types above
               DEFAULT   => ...,                           # any of the 3 value types above
               DEBUG     => ...;                           # boolean or coderef

       The INTEGER, FLOAT, NUMBER, STRING, SCALAR, ARRAY, HASH, CODE, UNDEF, DEFAULT and UNIVERSAL options
       can take three different types of value:

       •   A class name e.g.

               use autobox INTEGER => 'MyInt';

           This binds the specified native type to the specified class. All methods invoked on literals or
           values of type "key" will be dispatched as methods of the class specified in the corresponding
           "value".

       •   A namespace: this is a class prefix (up to and including the final '::') to which the specified
           type name (INTEGER, FLOAT, STRING &c.) will be appended:

           Thus:

               use autobox ARRAY => 'Prelude::';

           is equivalent to:

               use autobox ARRAY => 'Prelude::ARRAY';

       •   A reference to an array of class names and/or namespaces. This associates multiple classes with
           the specified type.

   DEFAULT
       The "DEFAULT" option specifies bindings for any of the four default types (SCALAR, ARRAY, HASH and
       CODE) not supplied in the "use autobox" statement. As with the other options, the "value"
       corresponding to the "DEFAULT" "key" can be a class name, a namespace, or a reference to an array
       containing one or more class names and/or namespaces.

       Thus:

           use autobox
               STRING  => 'MyString',
               DEFAULT => 'MyDefault';

       is equivalent to:

           use autobox
               STRING  => 'MyString',
               SCALAR  => 'MyDefault',
               ARRAY   => 'MyDefault',
               HASH    => 'MyDefault',
               CODE    => 'MyDefault';

       Which in turn is equivalent to:

           use autobox
               INTEGER => 'MyDefault',
               FLOAT   => 'MyDefault',
               STRING  => [ 'MyString', 'MyDefault' ],
               ARRAY   => 'MyDefault',
               HASH    => 'MyDefault',
               CODE    => 'MyDefault';

       Namespaces in DEFAULT values have the default type name appended, which, in the case of defaulted
       SCALAR types, is SCALAR rather than INTEGER, FLOAT &c.

       Thus:

           use autobox
               ARRAY   => 'MyArray',
               HASH    => 'MyHash',
               CODE    => 'MyCode',
               DEFAULT => 'MyNamespace::';

       is equivalent to:

           use autobox
               INTEGER => 'MyNamespace::SCALAR',
               FLOAT   => 'MyNamespace::SCALAR',
               STRING  => 'MyNamespace::SCALAR',
               ARRAY   => 'MyArray',
               HASH    => 'MyArray',
               CODE    => 'MyCode';

       Any of the four default types can be exempted from defaulting to the DEFAULT value by supplying a
       value of undef:

           use autobox
               HASH    => undef,
               DEFAULT => 'MyDefault';

           42->foo # ok: MyDefault::foo
           []->bar # ok: MyDefault::bar

           %INC->baz # not ok: runtime error

   UNDEF
       The pseudotype, UNDEF, can be used to autobox undefined values. These are not autoboxed by default.

       This doesn't work:

           use autobox;

           undef->foo() # runtime error

       This works:

           use autobox UNDEF => 'MyUndef';

           undef->foo(); # ok

       So does this:

           use autobox UNDEF => 'MyNamespace::';

           undef->foo(); # ok

   NUMBER, SCALAR and UNIVERSAL
       The virtual types NUMBER, SCALAR and UNIVERSAL function as macros or shortcuts which create bindings
       for their subtypes. The type hierarchy is as follows:

         UNIVERSAL -+
                    |
                    +- SCALAR -+
                    |          |
                    |          +- NUMBER -+
                    |          |          |
                    |          |          +- INTEGER
                    |          |          |
                    |          |          +- FLOAT
                    |          |
                    |          +- STRING
                    |
                    +- ARRAY
                    |
                    +- HASH
                    |
                    +- CODE

       Thus:

           use autobox NUMBER => 'MyNumber';

       is equivalent to:

           use autobox
               INTEGER => 'MyNumber',
               FLOAT   => 'MyNumber';

       And:

           use autobox SCALAR => 'MyScalar';

       is equivalent to:

           use autobox
               INTEGER => 'MyScalar',
               FLOAT   => 'MyScalar',
               STRING  => 'MyScalar';

       Virtual types can also be passed to "unimport" via the "no autobox" syntax. This disables autoboxing
       for the corresponding subtypes e.g.

           no autobox qw(NUMBER);

       is equivalent to:

           no autobox qw(INTEGER FLOAT);

       Virtual type bindings can be mixed with ordinary bindings to provide fine-grained control over
       inheritance and delegation. For instance:

           use autobox
               INTEGER => 'MyInteger',
               NUMBER  => 'MyNumber',
               SCALAR  => 'MyScalar';

       would result in the following bindings:

           42->foo             -> [ MyInteger, MyNumber, MyScalar ]
           3.1415927->bar      -> [ MyNumber, MyScalar ]
           "Hello, world!->baz -> [ MyScalar ]

       Note that DEFAULT bindings take precedence over virtual type bindings i.e.

           use autobox
               UNIVERSAL => 'MyUniversal',
               DEFAULT   => 'MyDefault'; # default SCALAR, ARRAY, HASH and CODE before UNIVERSAL

       is equivalent to:

         use autobox
             INTEGER => [ 'MyDefault', 'MyUniversal' ],
             FLOAT   => [ 'MyDefault', 'MyUniversal' ], # ... &c.

   DEBUG
       "DEBUG" exposes the current bindings for the scope in which "use autobox" is called by means of a
       callback, or a static debugging function.

       This allows the computed bindings to be seen in "longhand".

       The option is ignored if the value corresponding to the "DEBUG" key is false.

       If the value is a CODE ref, then this sub is called with a reference to the hash containing the
       computed bindings for the current scope.

       Finally, if "DEBUG" is true but not a CODE ref, the bindings are dumped to STDERR.

       Thus:

           use autobox DEBUG => 1, ...

       or

           use autobox DEBUG => sub { ... }, ...

       or

           sub my_callback ($) {
               my $hashref = shift;
               ...
           }

           use autobox DEBUG => \&my_callback, ...

METHODS
   import
       On its own, "autobox" doesn't implement any methods that can be called on native types.  However, its
       static method, "import", can be used to implement "autobox" extensions i.e.  lexically scoped modules
       that provide "autobox" bindings for one or more native types without requiring calling code to "use
       autobox".

       This is done by subclassing "autobox" and overriding "import". This allows extensions to effectively
       translate "use MyModule" into a bespoke "use autobox" call. e.g.:

           package String::Trim;

           use base qw(autobox);

           sub import {
               my $class = shift;
               $class->SUPER::import(STRING => 'String::Trim::Scalar');
           }

           package String::Trim::Scalar;

           sub trim {
               my $string = shift;
               $string =~ s/^\s+//;
               $string =~ s/\s+$//;
               $string;
           }

           1;

       Note that "trim" is defined in an auxiliary class rather than in "String::Trim" itself to prevent
       "String::Trim"'s own methods (i.e. the methods it inherits from "autobox") being exposed to SCALAR
       types.

       This module can now be used without a "use autobox" statement to enable the "trim" method in the
       current lexical scope. e.g.:

           #!/usr/bin/env perl

           use String::Trim;

           print "  Hello, world!  "->trim();

EXPORTS
   autobox_class
       "autobox" makes a single method available to autoboxed types: "autobox_class". This can be used to
       call "isa", "can", "VERSION", "import" and "unimport". e.g.

           if (42->autobox_class->isa('SCALAR')) ...
           if (sub { ... }->autobox_class->can('curry')) ...

   type
       "autobox" includes an additional module, "autobox::universal", which exports a single subroutine,
       "type".

       This sub returns the type of its argument within "autobox" (which is essentially longhand for the
       type names used within perl). This value is used by "autobox" to associate a method invocant with its
       designated classes. e.g.

           use autobox::universal qw(type);

           type("Hello, world!") # STRING
           type(42)              # INTEGER
           type([])              # ARRAY
           type(sub { })         # CODE

       "autobox::universal" is loaded automatically by "autobox", and, as its name suggests, can be used to
       install a universal method (i.e. a method for all "autobox" types) e.g.

           use autobox UNIVERSAL => 'autobox::universal';

           42->type        # INTEGER
           3.1415927->type # FLOAT
           %ENV->type      # HASH

CAVEATS
   Performance
       Autoboxing comes at a price. Calling

           "Hello, world!"->length()

       is slightly slower than the equivalent method call on a string-like object, and significantly slower
       than

           length("Hello, world!")

   Gotchas
       Precedence

       Due to Perl's precedence rules, some autoboxed literals may need to be parenthesized:

       For instance, while this works:

           my $curried = sub { ... }->curry();

       this doesn't:

           my $curried = \&foo->curry();

       The solution is to wrap the reference in parentheses:

           my $curried = (\&foo)->curry();

       The same applies for signed integer and float literals:

           # this works
           my $range = 10->to(1);

           # this doesn't work
           my $range = -10->to(10);

           # this works
           my $range = (-10)->to(10);

       print BLOCK

       Perl's special-casing for the "print BLOCK ..." syntax (see perlsub) means that "print { expression()
       } ..."  (where the curly brackets denote an anonymous HASH ref) may require some further
       disambiguation:

           # this works (
           print { foo => 'bar' }->foo();

           # and this
           print { 'foo', 'bar' }->foo();

           # and even this
           print { 'foo', 'bar', @_ }->foo();

           # but this doesn't
           print { @_ }->foo() ? 1 : 0

       In the latter case, the solution is to supply something other than a HASH ref literal as the first
       argument to "print()":

           # e.g.
           print STDOUT { @_ }->foo() ? 1 : 0;

           # or
           my $hashref = { @_ };
           print $hashref->foo() ? 1 : 0;

           # or
           print '', { @_ }->foo() ? 1 : 0;

           # or
           print '' . { @_ }->foo() ? 1 : 0;

           # or even
           { @_ }->print_if_foo(1, 0);

       eval EXPR

       Like most pragmas, autobox performs operations at compile time, and, as a result, runtime string
       "eval"s are not executed within its scope i.e. this doesn't work:

           use autobox;

           eval "42->foo";

       The workaround is to use autobox within the "eval" e.g.

           eval <<'EOS';
               use autobox;
               42->foo();
           EOS

       Note that the "eval BLOCK" form works as expected:

           use autobox;

           eval { 42->foo() }; # OK

VERSION
       2.75

SEE ALSO
       •   autobox::Core

       •   Moose::Autobox

       •   perl5i

       •   Scalar::Properties

AUTHOR
       chocolateboy <chocolate@cpan.org>

COPYRIGHT
       Copyright (c) 2003-2011, chocolateboy.

       This module is free software. It may be used, redistributed and/or modified under the same terms as
       Perl itself.



perl v5.12.5                                     2011-07-21                                       autobox(3)