typedef bool(*func)(int);
 
//template<typename T = int>
//class TC1{
//  public:
//      static  bool test_func(T t){
//          return true;
//      }
//};
 
template<typename T=int>
bool test_func(T){
    return true;
}
 
template< func f = &test_func>
class TC2{
    public:
        TC2(){
            //uncomment the line below ,compile will pass
            //test_func(3);
            f(3);
        }
};
 
template<typename T = char>
class TC3{
    public:
        TC2<> mc;
        TC3() = default;
};
 
int main(){
    TC3<> tc3;
    //uncomment the line below ,compile will pass
    //TC2<> mc;
}

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