Is there a reason declval returns add_rvalue_reference instead of add_lvalue_reference

Question

changing a type into a reference to a type, allows one to access the members of the type without creating an instance of the type. This seems to be true for bot

Answer 1

You want to be able to get back aT, a T&, or const/volatile qualified versions thereof. Since may not have a copy or move constructor, you can't just return the type, i.e., a reference needs to be returned. On the other hand, adding an rvalue teference to a reference type has no effect;

 std::declval  -> T&&
 std::declval -> T&

That is, adding an rvalue reference type has the effect of yielding a result which looks like an object of the passed type!