I've often wished for this in C and C++, particularly from an optimization perspective. I always hated that the optimizer cannot assume that the the contents of

I've often wished for this in C and C++, particularly from an optimization perspective. I always hated that the optimizer cannot assume that the the contents of a struct to which I have a const pointer won't change out from under me when I call another function. It means that it cannot cache members of this struct in callee-save registers; it has to reload them every time. I don't know how much of a speed difference it would actually make in practice, but it bothers me that I cannot express this in C++.