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Value Categories, Move and Perfect Forwarding · 3:37
Moves Aren't Free
A move is cheap only when there is a heap pointer to steal. We time a vector move against a std::array move (about a nanosecond against several microseconds on a Mac), look inside a std::string to see the small-string optimization keep short names in the handle itself, and catch the cases where a move silently becomes a copy: a user-declared destructor, a const source, and a move constructor that isn't noexcept.
You will learn
- Explain why moving a std::vector costs the same for any size while moving a std::array is linear
- Describe the small-string optimization and why short strings move no faster than they copy
- Recognise types whose std::move silently copies: user-declared destructors and const objects
- Explain why vector growth copies elements whose move constructor isn't noexcept