Without any compiler magic involved I don't think it's possible to implement that in C++ in a way compatible with the current std::string interface. The proble

Without any compiler magic involved I don't think it's possible to implement that in C++ in a way compatible with the current std::string interface. The problem is not the allocation of the std::string object itself, it's the allocation of the underlying buffer containing the string. std::string has a static size, the buffer itself is dynamically sized. You could replace the heap alloc with something like calloc (or dynamically sized arrays) in the constructor but then the buffer would be tied to the stack frame of the constructor, not the calling scope (so the memory would become invalid as soon as the constructor returns). Unless I'm missing something completely obvious the only way to implement that would be to ask for the caller to provide the buffer and let the string take ownership of it. It's definitely possible but it's not how std::string works and it's arguably more error-prone since unlike languages like rust there's no full blown lifetime checker in C++, so you'd have to make sure that the string object never outlives the supplied buffer. Alternatively you might be able to supply a custom allocator to std::strings but here be dragons.