Implement apply_traits

include/kumi/tuple.hpp

@@ -439,6 +439,30 @@ namespace kumi
   //================================================================================================
 }
 
+namespace kumi
+{
+  template< template<typename...> typename Traits
+          , product_type Tuple
+          , typename Seq = std::make_index_sequence<size<Tuple>::value>
+          >
+  struct apply_traits;
+
+  template< template<typename...> typename Traits
+          , product_type Tuple
+          , std::size_t... Is
+          >
+  requires( requires {typename Traits<element_t<Is,Tuple>...>::type;})
+  struct  apply_traits<Traits, Tuple, std::index_sequence<Is...>>
+  {
+    using type = typename Traits<element_t<Is,Tuple>...>::type;
+  };
+
+  template< template<typename...> typename Traits
+          , product_type Tuple
+          >
+  using apply_traits_t = typename apply_traits<Traits, Tuple>::type;
+}
+
 #include <kumi/algorithm.hpp>
 
 #undef KUMI_FWD

standalone/kumi/tuple.hpp

@@ -812,6 +812,27 @@ namespace kumi
   }
 }
 namespace kumi
+{
+  template< template<typename...> typename Traits
+          , product_type Tuple
+          , typename Seq = std::make_index_sequence<size<Tuple>::value>
+          >
+  struct apply_traits;
+  template< template<typename...> typename Traits
+          , product_type Tuple
+          , std::size_t... Is
+          >
+  requires( requires {typename Traits<element_t<Is,Tuple>...>::type;})
+  struct  apply_traits<Traits, Tuple, std::index_sequence<Is...>>
+  {
+    using type = typename Traits<element_t<Is,Tuple>...>::type;
+  };
+  template< template<typename...> typename Traits
+          , product_type Tuple
+          >
+  using apply_traits_t = typename apply_traits<Traits, Tuple>::type;
+}
+namespace kumi
 {
 }
 namespace kumi

test/unit/apply_traits.cpp

@@ -0,0 +1,65 @@
+//==================================================================================================
+/*
+  KUMI - Compact Tuple Tools
+  Copyright : KUMI Project Contributors
+  SPDX-License-Identifier: BSL-1.0
+*/
+//==================================================================================================
+#include "kumi/utils/concepts.hpp"
+#include <concepts>
+#include <type_traits>
+#define TTS_MAIN
+#include <kumi/tuple.hpp>
+#include <tts/tts.hpp>
+
+template<typename... T>
+struct nary_traits : std::integral_constant<std::size_t, std::max({sizeof(T)...})>
+{};
+
+TTS_CASE("Check apply_traits behavior")
+{
+  TTS_TYPE_IS ( (kumi::apply_traits_t < nary_traits
+                                      , kumi::tuple<int const, char, void*, float, double&, volatile short>
+                                      >)
+              , (std::integral_constant<std::size_t, 8>)
+              );
+};
+
+template<kumi::product_type T>
+kumi::apply_traits_t<nary_traits, T> f(T const&)
+{
+  return {};
+}
+
+template<kumi::product_type T>
+kumi::apply_traits_t<std::add_pointer, T> g(T const&)
+{
+  return {};
+}
+
+template<typename... T>
+requires( std::is_floating_point_v<T> && ...)
+struct strict_traits
+{
+  using type = bool;
+};
+
+template<kumi::product_type T>
+kumi::apply_traits_t<strict_traits, T> h(T const&)
+{
+  return true;
+}
+
+TTS_CASE("Check apply_traits SFINAE compliance")
+{
+  kumi::tuple<char,short,double> t;
+  kumi::tuple<float,double,float,double> u;
+
+  // wrong # of arguments to traits
+  TTS_EXPECT_COMPILES(t, { f(t); } );
+  TTS_EXPECT_NOT_COMPILES(t, { g(t); } );
+
+  // Unsupported types within tuple
+  TTS_EXPECT_COMPILES(u, { h(u); } );
+  TTS_EXPECT_NOT_COMPILES(t, { h(t); } );
+};