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  1. #include <iostream>
  2. #include <type_traits>
  3. #include <utility>
  4. #include <functional>
  5. #include <iostream>
  6. #include <string>
  7. #include <typeinfo>
  8.  
  9. template< class... > using void_t = void;
  10.  
  11. namespace impl
  12. {
  13.  
  14.   template <typename...>
  15.   struct callable_args
  16.   {
  17.   };
  18.  
  19.   template <class F, class Args, class = void>
  20.   struct callable : std::false_type
  21.   {
  22.   };
  23.  
  24.   template <class F, class... Args>
  25.   struct callable<F, callable_args<Args...>, void_t<std::result_of_t<F(Args...)>>> : std::true_type
  26.   {
  27.   };
  28.  
  29. }
  30.  
  31. template <class F, class... Args>
  32. struct callable : impl::callable<F, impl::callable_args<Args...>>
  33. {
  34. };
  35.  
  36. template <class F, class... Args>
  37. constexpr auto callable_v = callable<F, Args...>::value;
  38.  
  39.  
  40. int main()
  41. {
  42.   {
  43.     using Func = std::function<void()>;
  44.     auto result = callable_v<Func>;
  45.     std::cout << "test 1 (should be 1) = " << result << std::endl;
  46.   }
  47.  
  48.   {
  49.     using Func = std::function<void(int)>;
  50.     auto result = callable_v<Func, int>;
  51.     std::cout << "test 2 (should be 1) = " << result << std::endl;
  52.   }
  53.  
  54.   {
  55.     using Func = std::function<int(int)>;
  56.     auto result = callable_v<Func, int>;
  57.     std::cout << "test 3 (should be 1) = " << result << std::endl;
  58.   }
  59.  
  60.   {
  61.     using Func = std::function<int(double)>;
  62.     auto result = callable_v<Func, std::string>;
  63.     std::cout << "test 4 (should be 0) = " << result << std::endl;
  64.   }
  65.  
  66.   {
  67.     using Func = std::function<int(double, int)>;
  68.     auto result = callable_v<Func, double>;
  69.     std::cout << "test 5 (should be 0) = " << result << std::endl;
  70.   }
  71.  
  72.   std::getchar();
  73.  
  74.   return EXIT_SUCCESS;
  75. }
Success #stdin #stdout 0s 3472KB
comments (?)
stdin 
Standard input is empty
stdout 
test 1 (should be 1) = 1
test 2 (should be 1) = 1
test 3 (should be 1) = 1
test 4 (should be 0) = 0
test 5 (should be 0) = 0
https://ideone.com/EAbcga
language:
C++14 (gcc 8.3)
created:
9 years ago
visibility:
public

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