Can modern C++ get you performance for free?

Question

It is sometimes claimed that C++11/14 can get you a performance boost even when merely compiling C++98 code. The justification is usually along the lines of move semantics,

Answer 1

if you have something like:

std::vector foo(); // function declaration.
std::vector v;

// some code

v = foo();

You got a copy in C++03, whereas you got a move assignment in C++11. so you have free optimisation in that case.