Comment by knorker

What do you mean by "move or copy constructor is used when constructing the parameter of foo"?

Nothing is constructed at call time. Check out this example, which compiles just fine, even though Foo is neither copy nor move constructible/assignable: https://godbolt.org/z/Wj57o773d

"&&" is just a type system feature, resolving function polymorphism matching rvalue reference and not lvalue reference. It's not a thing that causes a move.