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  1. #include <type_traits>
  2. #include <utility>
  3.  
  4.     namespace util
  5.     {
  6.         template <typename T>
  7.         struct always_void
  8.         {
  9.             typedef void type;
  10.         };
  11.     }
  12.  
  13.     namespace detail
  14.     {
  15.         template <typename T, typename Args, typename Enable = void>
  16.         struct is_callable_impl
  17.           : std::false_type
  18.         {};
  19.  
  20.         template <typename T, typename... A>
  21.         struct is_callable_impl<T, void(A...)
  22.           , typename util::always_void<
  23.                 decltype(std::declval<T>()(std::declval<A>()...))
  24.             >::type
  25.         > : std::true_type
  26.         {};
  27.  
  28.         template <typename T, typename C>
  29.         struct is_callable_impl<T, void(C)
  30.             , typename util::always_void<
  31.                   decltype(
  32.                       (std::declval<typename std::remove_pointer<C>::type>()
  33.                           .*std::declval<T>()))
  34.               >::type
  35.         > : std::true_type
  36.         {};
  37.  
  38.         template <typename T, typename C, typename... A>
  39.         struct is_callable_impl<T, void(C, A...)
  40.             , typename util::always_void<
  41.                   decltype(
  42.                       (std::declval<typename std::remove_pointer<C>::type>()
  43.                           .*std::declval<T>())(std::declval<A>()...))
  44.               >::type
  45.         > : std::true_type
  46.         {};
  47.     }
  48.  
  49.     template <typename T, typename... A>
  50.     struct is_callable
  51.       : detail::is_callable_impl<T, void(A...)>
  52.     {};
  53.  
  54. struct X {};
  55.  
  56. int main()
  57. {
  58.     static_assert(is_callable<void (X::*)(int) const, X&, int>::value, "increment::call");
  59.  
  60.     auto lambda = [](){};
  61.     static_assert(is_callable<decltype(lambda)>::value, "");
  62.     static_assert(is_callable<void()>::value, "");
  63.  
  64.     static_assert(is_callable<int (X::*)(double), X*, float>::value, "");
  65.     static_assert(!is_callable<int (X::*)(double), X const*, float>::value, "");
  66.     static_assert(is_callable<int (X::*)(double), X&, float>::value, "");
  67.     static_assert(!is_callable<int (X::*)(double), X const&, float>::value, "");
  68.     static_assert(is_callable<int (X::*)(double) const, X*, float>::value, "");
  69.     static_assert(is_callable<int (X::*)(double) const, X const*, float>::value, "");
  70.     static_assert(is_callable<int (X::*)(double) const, X&, float>::value, "");
  71.     static_assert(is_callable<int (X::*)(double) const, X const&, float>::value, "");
  72.  
  73.     static_assert(is_callable<int (X::*), X*>::value, "");
  74.     static_assert(is_callable<int (X::*), X const*>::value, "");
  75.     static_assert(is_callable<int (X::*), X&>::value, "");
  76.     static_assert(is_callable<int (X::*), X const&>::value, "");
  77.     static_assert(is_callable<int (X::*), X&&>::value, "");
  78.     static_assert(is_callable<int (X::*), X const&&>::value, "");
  79.  
  80.     static_assert(!is_callable<void(int&), int>::value, "");
  81.     static_assert(is_callable<void(int&), int&>::value, "");
  82.     static_assert(!is_callable<void(int&), int const&>::value, "");
  83.     static_assert(!is_callable<void(int&), int&&>::value, "");
  84.     static_assert(!is_callable<void(int&), int const&&>::value, "");
  85.  
  86.     static_assert(is_callable<void(int const&), int>::value, "");
  87.     static_assert(is_callable<void(int const&), int&>::value, "");
  88.     static_assert(is_callable<void(int const&), int const&>::value, "");
  89.     static_assert(is_callable<void(int const&), int&&>::value, "");
  90.     static_assert(is_callable<void(int const&), int const&&>::value, "");
  91.  
  92.     static_assert(is_callable<void(int&&), int>::value, "");
  93.     static_assert(!is_callable<void(int&&), int&>::value, "");
  94.     static_assert(!is_callable<void(int&&), int const&>::value, "");
  95.     static_assert(is_callable<void(int&&), int&&>::value, "");
  96.     static_assert(!is_callable<void(int&&), int const&&>::value, "");
  97.  
  98.     static_assert(is_callable<void(int const&&), int>::value, "");
  99.     static_assert(!is_callable<void(int const&&), int&>::value, "");
  100.     static_assert(!is_callable<void(int const&&), int const&>::value, "");
  101.     static_assert(is_callable<void(int const&&), int&&>::value, "");
  102.     static_assert(is_callable<void(int const&&), int const&&>::value, "");
  103.  
  104.     return 0;
  105. }
  106.  
Success #stdin #stdout 0s 3292KB
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https://ideone.com/RzgXKM
language:
C++14 (gcc 8.3)
created:
11 years ago
visibility:
secret

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