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  1. #include <iostream>
  2.  
  3. template <typename Type> 
  4. class has_member 
  5. { 
  6.    class yes { char m;}; 
  7.    class no { yes m[2];}; 
  8.    struct BaseMixin 
  9.    { 
  10.      void operator()(){} 
  11.    }; 
  12.    struct Base : public Type, public BaseMixin {}; 
  13.    template <typename T, T t>  class Helper{}; 
  14.    template <typename U> 
  15.    static no deduce(U*, Helper<void (BaseMixin::*)(), &U::operator()>* = 0); 
  16.    static yes deduce(...); 
  17. public: 
  18.    static const bool result = sizeof(yes) == sizeof(deduce((Base*)(0))); 
  19. };
  20.  
  21. struct A{};
  22. struct B{ void operator()(){} };
  23. struct C{ void operator()(int,int){} };
  24.  
  25. int main() 
  26. {	
  27.  
  28.    std::cout << std::boolalpha; //so that true or false will be printed instead of 1 or 0
  29.  
  30.    std::cout << has_member<A>::result << std::endl;
  31.    std::cout << has_member<B>::result << std::endl;
  32.    std::cout << has_member<C>::result << std::endl;
  33. }
Success #stdin #stdout 0.01s 2724KB
comments (?)
stdin
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Standard input is empty
stdout
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false
true
true
https://ideone.com/wWpaP
language:
C++ (gcc 8.3)
created:
12 years ago
visibility:
public

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