fork download

#include <type_traits>
 
class A {};
 
class B: public A {};
 
class C: public B {};
 
class X {};
 
template<typename T, typename Base,
    typename = typename std::enable_if<
        std::is_base_of<std::decay_t<Base>, std::decay_t<T>>::value>::type>
void foo(T& tp, const Base* bp);
 
int main()
{
	A a; B b; C c; X x;
	foo(c, &a);
	foo(b, &a);
	foo(a, &a);
 
	foo(c, &b);
 
	foo(c, &c);
 
	foo(x, &a); // invalid and produces compiler error
}

prog.cpp: In function 'int main()':
prog.cpp:27:11: error: no matching function for call to 'foo(X&, A*)'
  foo(x, &a); // invalid and produces compiler error
           ^
prog.cpp:27:11: note: candidate is:
prog.cpp:14:6: note: template<class T, class Base, class> void foo(T&, const Base*)
 void foo(T& tp, const Base* bp);
      ^
prog.cpp:14:6: note:   template argument deduction/substitution failed:
prog.cpp:12:5: error: no type named 'type' in 'struct std::enable_if<false, void>'
     typename = typename std::enable_if<
     ^

Standard output is empty