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  1. #include <tuple>
  2. #include <type_traits>
  3.  
  4.     template <template <class> class,
  5.               template <class...> class,
  6.               class...>
  7.     struct filter;
  8.     template <template <class> class Pred, template <class...> class Variadic>
  9.     struct filter<Pred, Variadic>
  10.     {
  11.         using type = Variadic<>;
  12.     };
  13.  
  14.     template <template <class> class Pred,
  15.               template <class...> class Variadic,
  16.               class T, class... Ts>
  17.     struct filter<Pred, Variadic, T, Ts...>
  18.     {
  19.         template <class, class> struct Cons;
  20.         template <class Head, class... Tail>
  21.         struct Cons<Head, Variadic<Tail...> >
  22.         {
  23.             using type = Variadic<Head, Tail...>;
  24.         };
  25.  
  26.         using type = typename std::conditional<
  27.             Pred<T>::value,
  28.             typename Cons<T, typename filter<Pred, Variadic, Ts...>::type>::type,
  29.             typename filter<Pred, Variadic, Ts...>::type >::type;
  30.     };
  31.  
  32. int main() {
  33. 	    static_assert(std::is_same<
  34.                   filter<std::is_integral, std::tuple, int, float, long>::type,
  35.                   std::tuple<int, long> >::value, "");
  36. }
Success #stdin #stdout 0s 4492KB
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https://ideone.com/MzUtL6
language:
C++14 (gcc 8.3)
created:
4 years ago
visibility:
public

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