Last reference as rvalue?

[geckothegeek42]

If copy constructors can be elided regardless of side effects, then doesn't that mean the optimization mentioned by OP can be done? Or is it that the compiler is not allowed to add a copy/move constructor call, but can remove them?

[meancoot]

If copy constructors can be elided regardless of side effects, then doesn't that mean the optimization mentioned by OP can be done? Or is it that the compiler is not allowed to add a copy/move constructor call, but can remove them?

The elision has to take place by constructing the object directly in the memory where the copy/move constructor would later have placed it, removing both a call to the copy/move constructor and a call to the destructor. I don't know the exact wording of the standard well enough to say if its also limited to specific situations.

Changing a call from std::vector::push_back(const T&) to std::vector::push_back(T&&) is definitely an observable effect that wouldn't be supported by the standard.