#include <iostream>
#include <functional>

using YES = char;
struct NO { YES m[2]; };

template<typename T>
struct Method {};

template<>
struct Method<int> {
    int operator()() { return 1; }
};

template<class T>
struct is_brackets_op_defined {
  static void Check(...);

  template<typename C>
  static decltype(Method<C>::()) Check(const C&);

  using type = decltype(Check(
    std::declval< Method<T> >()
  ));

  constexpr static bool value =
    !std::is_same<void, type>();
};

int main() {
    std::cout << is_brackets_op_defined<float>::value << std::endl;
}