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  1. #include <type_traits>
  2. #include <utility>
  3. #include <iostream>
  4.  
  5. template <typename T, typename = void>
  6. struct foo_impl {};
  7.  
  8. template <typename T>
  9. inline auto foo(T x) -> decltype(foo_impl<T>{}(x))
  10. {
  11.         return foo_impl<T>{}(x);
  12. }
  13.  
  14. template <typename T>
  15. struct foo_impl<T,typename std::enable_if<std::is_integral<T>::value>::type>
  16. {
  17.         void operator()(T) {}
  18. };
  19.  
  20. template <typename T>
  21. struct has_foo
  22. {
  23.         struct yes {};
  24.         struct no {};
  25.         template <typename T1>
  26.         static auto test(T1 x) -> decltype(foo(x),void(),yes{});
  27.         static no test(...);
  28.         static const bool value = std::is_same<yes,decltype(test(std::declval<T>()))>::value;
  29. };
  30.  
  31. template <typename T>
  32. struct foo_impl<T,typename std::enable_if<has_foo<unsigned>::value && std::is_floating_point<T>::value>::type>
  33. {
  34.         void operator()(T) {}
  35. };
  36.  
  37. int main()
  38. {
  39.         std::cout << has_foo<float>::value << '\n';
  40.         std::cout << has_foo<int>::value << '\n';
  41.         foo(3.1);
  42. }
Success #stdin #stdout 0s 3468KB
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https://ideone.com/XClvYT
language:
C++14 (gcc 8.3)
created:
8 years ago
visibility:
public

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