The compiler is not required to perform RVO/NRVO and when it can be done depends on some surprising things such as the calling convention of the machine you are

The compiler is not required to perform RVO/NRVO and when it can be done depends on some surprising things such as the calling convention of the machine you are targeting. It's just an optimization the standard allows compilers to do (eliding copies). What C++11 provides is a new kind of type that says "it is safe to steal the guts of this value". You can use this to overload a copy constructor or assignment operator to do "moves" instead of "copies". Because it is baked into the type system, it is guaranteed to happen when you expect it. While eliding a copy essentially has 0 cost, and the compiler will still prefer this over a move, moving a vector can have a very small cost (copying a few pointers), but it is still O(1) instead of O(n).