Why does this need an explicit std::move?

Question

Let\'s say I got a Foo class containing an std::vector constructed from std::unique_ptr objects of another class, Bar.

Answer 1

Basically, every object which has a name is an lvalue. When you pass an object to a function using an rvalue reference the function actually sees an lvalue: it is named. What the rvalue reference does, however, indicate is that it came from an object which is ready to be transferred.

Put differently, rvalue references are assymmetrical:

• they can only receive rvalues, i.e., either temporary objects, objects about to go away, or objects which look as if they are rvalues (e.g., the result of std::move(o))
• the rvalue reference itself looks, however, like an lvalue