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  1. #include <iostream>
  2. #include <utility>
  3. #include <type_traits>
  4.  
  5.     namespace details {
  6.       template<class...>struct types{using type=types;};
  7.       template<class U, class Types, class=void>
  8.       struct smart_cast_t:std::false_type {
  9.         using type=U;
  10.         template<class A>
  11.         U operator()(A&& a)const{return std::forward<A>(a);}
  12.       };
  13.       template<class U, class T0, class...Ts>
  14.       struct smart_cast_t<
  15.         U, types<T0, Ts...>,
  16.         typename std::enable_if<std::is_convertible<U, T0>::value>::type
  17.       >:std::true_type
  18.       {
  19.         using type=T0;
  20.         template<class A>
  21.         T0 operator()(A&& a)const{return std::forward<A>(a);}
  22.       };
  23.       template<class U, class T0, class...Ts>
  24.       struct smart_cast_t<
  25.         U, types<T0, Ts...>,
  26.         typename std::enable_if<!std::is_convertible<U, T0>::value>::type
  27.       >:smart_cast_t< U, types<Ts...> >
  28.       {};
  29.     }
  30.  
  31.     template<class... Ts, class U>
  32.     auto smart_cast( U&& u )
  33.     -> decltype(details::smart_cast_t< U, details::types<Ts...> >{}( std::forward<U>(u) ))
  34.     {
  35.       return details::smart_cast_t< U, details::types<Ts...> >{}( std::forward<U>(u) );
  36.     }
  37.  
  38. int main() {
  39. 	std::cout << smart_cast< char, double >( int('a') ) << "\n";
  40. 	std::cout << smart_cast< double, char >( int('a') ) << "\n";
  41. 	// your code goes here
  42. 	return 0;
  43. }
Success #stdin #stdout 0s 3296KB
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a
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https://ideone.com/FZB4K1
language:
C++14 (gcc 8.3)
created:
10 years ago
visibility:
public

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