I like the use of explicit std::move to specify intent at the callsite. I'd love the same for std::copy, as in: a = std::copy(b). Right now my containers/etc have a copy_from method with implicit copies disabled, but I'm sure I could engineer something trivial for this.
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You are not specifying the intent at the call site because in most cases explicitly moving an lvalue is a bug or a potential bug. For example: return std::move(foo); // RVO broken, you just converted a noop into a move Foo foo; f(std::move(foo)); // foo still alive, but broken
This is a bit of an aside, but while your first case is certainly better just as RVO, the second case is perfectly fine and encouraged in certain cases. Example: Functions that intend to “clone and own” arguments should take by value and let the caller decide move or copy.
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Only if the function doing that acts like a "sink": f(A a) if condition return g(move(a)) else mutateA(a) ... saveA(move(a)) No dangling moved object used in any branch
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Yes. Definitely what I meant by clone and own.
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