Code for Dev.to C++ Templates and SFINAE

dev_article_sfinae.cpp

#include <iostream>
#include <type_traits>

template <class T>
class check_new_interface {
  template <class R>
  static auto check(int) -> decltype(std::declval<R>().getValue(0, 0));

  template <class>
  static double check(double);

 public:
  static constexpr bool value = sizeof(decltype(check<T>(0))) == sizeof(int);
};

class SupportedBackend {
 public:
  int getValue(int data1, int data2) { return data1 + data2; }
};

class UnsupportedBackend {
 public:
  int getValue(int data) { return data + 1; }
};

// template <typename Backend>
// class Container {
//  private:
//   Backend b;
//   int data;
//   int data1, data2;

//  public:
//   Container(int data, int data1, int data2)
//       : data(data), data1(data1), data2(data2) {}
//   int get() { return b.getValue(data); }
// };

template <typename Backend>
class Container {
 private:
  Backend b;
  int data;
  int data1, data2;

  inline int get(std::false_type) { return b.getValue(data); }

  inline int get(std::true_type) { return b.getValue(data1, data2); }

 public:
  Container(int data, int data1, int data2)
      : data(data), data1(data1), data2(data2) {}

  int get() {
    return get(
        std::integral_constant<bool, check_new_interface<Backend>::value>());
  }
};

int main() {
  Container<UnsupportedBackend> A(1, 2, 3);
  Container<SupportedBackend> B(1, 2, 3);
  std::cout << A.get() << std::endl;
  std::cout << B.get() << std::endl;
  return 0;
}