contains_foo_type

#include<bits/stdc++.h>
using namespace std;

template<class T>
struct contains_foo_type{
    typedef int true_type;
    typedef char false_type;
    template<class S>
    static true_type f(typename S::foo_type* a);
    template<class S>
    static false_type f(...);
    static const bool value=sizeof(f<T>(0))==sizeof(true_type);
};

struct A{};
struct B{typedef int foo_type;};
struct C{int foo_type;};

int main(){
    printf("%d\n",contains_foo_type<A>::value);
    printf("%d\n",contains_foo_type<B>::value);
    printf("%d\n",contains_foo_type<C>::value);
}