std::unreachable

`<utility>`
`[[noreturn]] void unreachable();`		( C++23)

. ( ) , ( ).


`__cpp_lib_unreachable`	`202202L`	(C++23)	`std::unreachable`

[[noreturn]] inline void unreachable()
{
    //       .
    //     ,   
    //        noreturn.
#ifdef __GNUC__ // GCC, Clang, ICC
    __builtin_unreachable();
#elifdef _MSC_VER // MSVC
    __assume(false);
#endif
}

#include <vector>
#include <cassert>
#include <cstddef>
#include <cstdint>
#include <utility>

struct Color { std::uint8_t r, g, b, a; };

// ,       .
void generate_texture(std::vector<Color>& tex, std::size_t xy)
{
    switch (xy) {
    case 128: [[fallthrough]];
    case 256: [[fallthrough]];
    case 512: /* ... */
        tex.clear();
        tex.resize(xy * xy, Color{0, 0, 0, 0});
        break;
    default:
        std::unreachable();
    }
}

int main()
{
    std::vector<Color> tex;
    generate_texture(tex, 128); // OK
    assert(tex.size() == 128 * 128);
    generate_texture(tex, 32);  //    
}

:

Segmentation fault

`assume]]` (C++23)	, `true` ( )[]
assume_aligned (C++20)	, ( ) []
C unreachable

1.	GCC: `__builtin_unreachable`
2.	Clang: `__builtin_unreachable`
3.	MSVC: `__assume`







(C++20)

(C++20)
(C++11)





(C++20)


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(C++11)
(C++11)
(C++11)
(C++17)

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std::unreachable