fork download 
  1. #include <iostream>
  2.  
  3. template <typename T = void>
  4. class Class {
  5. public:
  6. 	template <
  7. 		typename U,
  8. 		typename = typename std::enable_if<
  9. 			// Is the use of T here allowed?
  10. 			std::is_void<T>::value
  11. 			|| std::is_base_of<T, U>::value
  12. 		>::type
  13. 	>
  14. 	Class(U &&arg) {
  15. 		std::cout << "Derived" << std::endl;
  16. 	}
  17.  
  18. 	template <
  19. 		typename U,
  20. 		typename ...U_Rest,
  21. 		typename = typename std::enable_if<
  22. 			// Is the use of T here allowed?
  23. 			!std::is_void<T>::value
  24. 			&& !std::is_base_of<T, U>::value
  25. 		>::type
  26. 	>
  27. 	Class(U &&arg, U_Rest &&...rest) {
  28. 		std::cout << "Not Derived" << std::endl;
  29. 	}
  30. };
  31.  
  32. class Base { };
  33. class Derived : public Base { };
  34.  
  35. int main() {
  36. 	// Initialize with derived.
  37. 	Class<Base> c0 { Derived() };
  38. 	// Initialize with not derived.
  39. 	Class<Derived> c1 { Base() };
  40. 	// Use same constructor as if derived.
  41. 	Class<> c2 { Derived() };
  42. }
  43.  
Success #stdin #stdout 0s 3468KB
comments (?)
stdin 
Standard input is empty
stdout 
Derived
Not Derived
Derived
https://ideone.com/jmGDLv
language:
C++14 (gcc 8.3)
created:
8 years ago
visibility:
public

Share or Embed source code

Discover > Sphere Engine API

The brand new service which powers Ideone!

Discover > IDE Widget

Widget for compiling and running the source code in a web browser!