So you are saying that the buffer would be allocated in the program in A::init_from_file? And the compiler would be able to optimise that away by allocating the

So you are saying that the buffer would be allocated in the program in A::init_from_file? And the compiler would be able to optimise that away by allocating the buffer outside the loop? If the compiler actually does that, that would be a good example. As long as I don't have to be careful to write my code in a way that some obscure compiler optimisation understands.