Try this:
#include <type_traits>
template <typename T, template <typename> class Tmpl> // #1 see note
struct is_derived
{
typedef char yes[1];
typedef char no[2];
static no & test(...);
template <typename U>
static yes & test(Tmpl<U> const &);
static bool const value = sizeof(test(std::declval<T>())) == sizeof(yes);
};
Usage:
#include <iostream>
template<class T> struct X {};
struct A : X<int> {};
int main()
{
std::cout << is_derived<A, X>::value << std::endl;
std::cout << is_derived<int, X>::value << std::endl;
}
Note: In the line marked #1
, you could also make your trait accept any template that has at least one, but possibly more type arguments by writint:
template <typename, typename...> class Tmpl