std::meta::has_unique_object_representations

#include <cstdint>
#include <meta>

struct unpadded
{
    std::uint32_t a, b;
};

struct likely_padded
{
    std::uint8_t c;
    std::uint16_t st;
    std::uint32_t i;
};

int main()
{
    // Every value of a char corresponds to exactly one object representation.
    static_assert(has_unique_object_representations(^^char));

    // For IEC 559 floats, assertion passes because the
    // value NaN has multiple object representations.
    static_assert(!has_unique_object_representations(^^float));
    
    // Should succeed in any sane implementation because ‘unpadded’ is
    // typically not padded, and std::uint32_t cannot contain padding bits.
    static_assert(has_unique_object_representations(^^unpadded));

    // Fails in most implementations because padding bits are inserted between
    // the data members ‘c’ and ‘st’ for the purpose of aligning ‘st’ to 16 bits.
    static_assert(!has_unique_object_representations(^^likely_padded));
    
    // Notable architectural divergence:
    static_assert(has_unique_object_representations(^^bool)); // x86
    // static_assert(!has_unique_object_representations(^^bool)); // ARM
}