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Value Categories, Move and Perfect Forwarding · 4:00
move vs forward, and Return Value Optimization
std::move is an unconditional cast for rvalue references; std::forward<T> is a conditional cast for forwarding references, used once at the last use. We watch std::move on a forwarding reference empty the caller's string, then count constructions to show why `return std::move(w)` only adds a move that the return value optimization would have avoided.
You will learn
- Choose std::move for rvalue references and std::forward<T> for forwarding references
- Explain how std::forward<T> decides between lvalue and rvalue from the deduced T
- Apply move/forward only at an argument's last use
- Explain return value optimization and why `return std::move(local)` is a pessimization