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  1. #include <type_traits>
  2.  
  3. template<typename...>
  4. using void_type = void;
  5.  
  6. template <typename, typename, typename = void_type<>>
  7. struct CheckHelper: std::false_type {};
  8.  
  9. template <typename T, typename Base>
  10. struct CheckHelper<T, Base, void_type<typename std::enable_if<std::is_same<T, std::nullptr_t>::value, void>::type>> : std::true_type {};
  11.  
  12. template <typename T, typename Base, typename = void_type<>>
  13. struct CheckFun: CheckHelper<T, Base> {};
  14.  
  15. template <typename T, typename Base>
  16. struct CheckFun<T, Base, void_type<typename std::enable_if<!std::is_same<decltype(&T::fun), decltype(&Base::fun)>::value, void>::type>> : std::true_type {};
  17.  
  18. template<typename T = std::nullptr_t>
  19. class Base {
  20. public:
  21. 	virtual void fun() {
  22. 		static_assert(CheckFun<T, Base>::value, "Class T shoul override fun");
  23.  
  24. 	}
  25. };
  26.  
  27. class Derived1: public Base<Derived1> {
  28. public:
  29. 	void fun() override {
  30.  
  31. 	}
  32. };
  33.  
  34. class Derived2: public Base<Derived2> {
  35. };
  36.  
  37.  
  38. int main() {
  39. 	Base<> b{};
  40. 	Derived1 d1{};
  41. 	Derived2 d2{};
  42. 	d2.fun();
  43. }
Compilation error #stdin compilation error #stdout 0s 4388KB
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Standard input is empty
compilation info 
prog.cpp:22:3: error: static_assert failed "Class T shoul override fun"
                static_assert(CheckFun<T, Base>::value, "Class T shoul override fun");
                ^             ~~~~~~~~~~~~~~~~~~~~~~~~
prog.cpp:42:5: note: in instantiation of member function 'Base<Derived2>::fun' requested here
        d2.fun();
           ^
1 error generated.
stdout
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Standard output is empty
https://ideone.com/FPDCq0
language:
C++14 (clang 8.0)
created:
6 years ago
visibility:
public

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