C++: What is std::out_ptr (C++23)?

1#include <memory>
2
3// C API: void create(Handle* handle);
4extern "C" void create_c_handle(void** handle);
5extern "C" void destroy_c_handle(void* handle);
6
7// Manual (error-prone)
8void* raw = nullptr;
9create_c_handle(&raw);
10std::unique_ptr<void, decltype(&destroy_c_handle)> handle(raw, destroy_c_handle);
11
12// With std::out_ptr (clean)
13std::unique_ptr<void, decltype(&destroy_c_handle)> handle(
14    nullptr, destroy_c_handle
15);
16create_c_handle(std::out_ptr(handle));
17
18// Works with any smart pointer
19std::unique_ptr<int> uptr;
20// C function: void fill(int** ptr);
21// fill(std::out_ptr(uptr));  // Sets uptr
22
23// Reset on exception
24auto safe = [&] {
25    std::unique_ptr<void, decltype(&destroy_c_handle)> h(
26        nullptr, destroy_c_handle
27    );
28    create_c_handle(std::out_ptr(h));
29    return h;  // Automatically cleaned up on exception
30};