Why does C++11 have implicit moves for value parameters, but not for rvalue parameters?

Question

In C++11, value parameters (and other values) enjoy implicit move when returned:

A func(A a) {
    return a; // uses A::A(A&&) if it exists
}
         


        

Answer 1

This was fixed for C++20 by P0527 and P1825. The only way to have a function parameter bind to an rvalue reference is for the source to either be a temporary or for the caller to explicitly cast a non-temporary to an rvalue (for instance, with std::move). Therefore, this "mandatory optimization" was deemed safe.