> So you're telling me that in C++ you can't reliably implement a userspace mmap (or even use normal mmap) implementation before C++23 because without std::star

> So you're telling me that in C++ you can't reliably implement a userspace mmap (or even use normal mmap) implementation before C++23 because without std::start_lifetime_as the C++ abstract machine doesn't provide a way of specifying when an object's lifetime starts? std::start_lifetime_as is just a nice wrapper around an older incantation: do a no-op memmove and cast followed by a constant-folding barrier. C allows type punning with unions but I would assume the constant-folding issue would still exist. Compilers finally became clever enough about constant-folding to cause problems when you reinterpret the type at runtime.