#include #include namespace cs { template < typename... Element > struct typelist {}; template < typename List > struct front; template < typename Head, typename... Tail > struct front< typelist< Head, Tail... > > { using type = Head; }; template < typename List > using front_t = typename front< List >::type; template < typename List > struct pop_front; template < typename Head, typename... Tail > struct pop_front< typelist< Head, Tail... > > { using type = typelist< Tail... >; }; template < typename List > using pop_front_t = typename pop_front< List >::type; template < typename List > struct is_empty { static constexpr bool value{ false }; }; template <> struct is_empty< typelist<> > { static constexpr bool value{ true }; }; template < typename List > inline constexpr bool is_empty_v = is_empty< List >::value; // IS_SORTED - START template < typename List, template < typename T1, typename T2 > typename Compare, bool Accumulator = false, bool Empty = is_empty_v< List > > struct is_sorted_implementation; template < typename List, template < typename T1, typename T2 > typename Compare > struct is_sorted_implementation< List, Compare, false, false > : public std::conditional_t< is_empty_v< pop_front_t< List > >, is_sorted_implementation< pop_front_t< List >, Compare, false >, is_sorted_implementation< pop_front_t< List >, Compare, Compare< front_t< pop_front_t< List > >, front_t< List > >::value > > {}; template < typename List, template < typename T1, typename T2 > typename Compare > struct is_sorted_implementation< List, Compare, true, false > { static constexpr bool value{ false }; }; template < typename List, template < typename T1, typename T2 > typename Compare > struct is_sorted_implementation< List, Compare, true, true > { static constexpr bool value{ true }; }; template < typename List, template < typename T1, typename T2 > typename Compare > struct is_sorted_implementation< List, Compare, false, true > { static constexpr bool value{ true }; }; template < typename List, template < typename T1, typename T2 > typename Compare > struct is_sorted : public is_sorted_implementation< List, Compare > {}; template < typename List, template < typename T1, typename T2 > typename Compare > inline constexpr bool is_sorted_v = is_sorted< List, Compare >::value; // IS_SORTED - END } // namespace cs template < typename T1, typename T2 > struct less { static constexpr bool value{ sizeof( T1 ) < sizeof( T2 ) }; }; int main() { using namespace cs; std::cout << is_sorted_v< typelist<>, less > << std::endl; // fails // std::cout << is_sorted_v< typelist< int >, less > << std::endl; // std::cout << is_sorted_v< typelist< char, int >, less > << std::endl; return 0; }

[Q&A] is_sorted<>