Why does std::is_assignable return false with related pointer types?

Question

Given two very simple classes:

class X { };  class Y : public X { }; 

Why is it that, with Clang and GCC targeting C++14, std::is_assignable<X*, Y*>::value is false? It is true with Clang on my setup when I target C++11.

Answer 1

This is because in your case X* becomes an rvalue. You can't assign to an rvalue. Change to an lvalue instead:

std::is_assignable<X*&, Y*>::value //                  ~^~