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  1. #include <iostream>
  2.  
  3. template <typename T>
  4. struct is_foo {
  5.     private:
  6.         template<typename U, U> struct helper{};
  7.  
  8.         template <typename Z> static auto test(Z z) -> decltype(
  9.  
  10.                 helper<void (Z::*)() const,                       &Z::foo>(),
  11.                 // All other requirements follow..
  12.  
  13.                 std::true_type()
  14.                 );
  15.  
  16.         template <typename> static auto test(...) -> std::false_type;
  17.  
  18.     public:
  19.         enum { value = std::is_same<decltype(test<T>(std::declval<T>())),std::true_type>::value };
  20. };
  21.  
  22. struct A { 
  23.     void foo() const; 
  24. };
  25.  
  26. struct A1 : public A {};
  27.  
  28. struct B { void foo(); };
  29. struct C { int foo() const; };
  30.  
  31. template <typename T>
  32. struct D : public T {};
  33.  
  34. int main() {
  35.     std::cout << "Good examples (should print 1)\n";
  36.     std::cout << is_foo<A>::value       << '\n';    
  37.     std::cout << is_foo<A1>::value      << '\n';   
  38.     std::cout << is_foo<D<A>>::value    << '\n'; 
  39.     std::cout << is_foo<D<A1>>::value   << '\n';
  40.  
  41.     std::cout << "Bad examples (should print 0)\n";
  42.     std::cout << is_foo<B>::value       << '\n';
  43.     std::cout << is_foo<C>::value       << '\n';
  44.     std::cout << is_foo<D<B>>::value    << '\n';
  45.     std::cout << is_foo<D<C>>::value    << '\n';
  46.  
  47.     return 0;
  48. }
  49.  
Success #stdin #stdout 0s 3296KB
comments (?)
stdin
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Standard input is empty
stdout
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Good examples (should print 1)
1
0
0
0
Bad examples (should print 0)
0
0
0
0
https://ideone.com/mxIVw3
language:
C++14 (gcc 8.3)
created:
11 years ago
visibility:
public

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