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#include <tuple>
#include <type_traits>
 
    template <template <class> class,
              template <class...> class,
              class...>
    struct filter;
    template <template <class> class Pred, template <class...> class Variadic>
    struct filter<Pred, Variadic>
    {
        using type = Variadic<>;
    };
 
    template <template <class> class Pred,
              template <class...> class Variadic,
              class T, class... Ts>
    struct filter<Pred, Variadic, T, Ts...>
    {
        template <class, class> struct Cons;
        template <class Head, class... Tail>
        struct Cons<Head, Variadic<Tail...> >
        {
            using type = Variadic<Head, Tail...>;
        };
 
        using type = typename std::conditional<
            Pred<T>::value,
            Cons<T, filter<Pred, Variadic, Ts...>::type>::type,
            filter<Pred, Variadic, Ts...>::type >::type;
    };
 
int main() {
	    static_assert(std::is_same<
                  filter<std::is_integral, std::tuple, int, float, long>::type,
                  std::tuple<int, long> >::value, "");
}

prog.cpp:28:56: error: type/value mismatch at argument 2 in template parameter list for ‘template<template<class> class Pred, template<class ...> class Variadic, class T, class ... Ts> template<class, class> struct filter<Pred, Variadic, T, Ts ...>::Cons’
             Cons<T, filter<Pred, Variadic, Ts...>::type>::type,
                                                        ^
prog.cpp:28:56: error:   expected a type, got ‘filter<Pred, Variadic, Ts ...>::type’
prog.cpp:29:49: error: template argument 2 is invalid
             filter<Pred, Variadic, Ts...>::type >::type;
                                                 ^
prog.cpp:29:49: error: type/value mismatch at argument 3 in template parameter list for ‘template<bool <anonymous>, class, class> struct std::conditional’
prog.cpp:29:49: error:   expected a type, got ‘filter<Pred, Variadic, Ts ...>::type’
prog.cpp: In function ‘int main()’:
prog.cpp:34:19: error: ‘type’ is not a member of ‘filter<std::is_integral, std::tuple, int, float, long int>’
                   filter<std::is_integral, std::tuple, int, float, long>::type,
                   ^
prog.cpp:34:19: error: ‘type’ is not a member of ‘filter<std::is_integral, std::tuple, int, float, long int>’
prog.cpp:35:41: error: template argument 1 is invalid
                   std::tuple<int, long> >::value, "");
                                         ^

Standard output is empty