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Value Categories, Move and Perfect Forwarding · 4:15
std::move Moves Nothing
std::move sounds like it moves, but it is only a cast that relabels an object as an rvalue; the stealing happens later, if a move constructor or move assignment acts on that label. We check that it compiles to no instructions at all, see why a named rvalue-reference parameter is still an lvalue, watch a const object silently get copied instead of moved, and finish with the Annotation trap and the rules for moved-from objects.
You will learn
- Explain that std::move is a cast to an rvalue reference and generates no code
- Recognise that a named rvalue-reference parameter is an lvalue, and apply std::move at its last use
- Predict that std::move on a const object selects the copy constructor
- Treat a moved-from object as valid but unspecified: assign it before reading it