Use a std::apply style unpack

* Some cleanup

include/continuable/continuable-base.hpp

@@ -852,8 +852,8 @@ constexpr auto make_ready_continuable(FirstResult&& first_result,
                                 std::forward<SecondResult>(second_result),
                                 std::forward<Rest>(rest)...)](
           auto&& promise) mutable {
-        detail::traits::unpack(result,
-                               std::forward<decltype(promise)>(promise));
+        detail::traits::unpack(std::forward<decltype(promise)>(promise),
+                               result);
       });
 }
 

include/continuable/detail/base.hpp

@@ -231,12 +231,14 @@ inline auto sequenced_unpack_invoker() {
       // the lambda.
       using Next = decltype(next_callback);
 
-      traits::unpack(std::move(result), [&](auto&&... types) {
-        /// TODO Add inplace resolution here
+      traits::unpack(
+          [&](auto&&... types) {
+            /// TODO Add inplace resolution here
 
-        invoke_no_except(std::forward<Next>(next_callback),
-                         std::forward<decltype(types)>(types)...);
-      });
+            invoke_no_except(std::forward<Next>(next_callback),
+                             std::forward<decltype(types)>(types)...);
+          },
+          std::move(result));
     CONTINUABLE_BLOCK_TRY_END
   };
 } // namespace decoration
@@ -277,12 +279,15 @@ void packed_dispatch(Executor&& executor, Invoker&& invoker, Args&&... args) {
     invoker = std::forward<Invoker>(invoker),
     args = std::make_tuple(std::forward<Args>(args)...)
   ]() mutable {
-    traits::unpack(std::move(args), [&](auto&&... captured_args) {
-      // Just use the packed dispatch method which dispatches the work on
-      // the current thread.
-      packed_dispatch(types::this_thread_executor_tag{}, std::move(invoker),
-                      std::forward<decltype(captured_args)>(captured_args)...);
-    });
+    traits::unpack(
+        [&](auto&&... captured_args) {
+          // Just use the packed dispatch method which dispatches the work on
+          // the current thread.
+          packed_dispatch(
+              types::this_thread_executor_tag{}, std::move(invoker),
+              std::forward<decltype(captured_args)>(captured_args)...);
+        },
+        std::move(args));
   };
 
   // Pass the work callable object to the executor

include/continuable/detail/connection-aggregated.hpp

@@ -149,9 +149,11 @@ public:
   }
 
   auto unbox() && {
-    return traits::unpack(unpack_lazy(std::move(args_)), [](auto&&... args) {
-      return spread_this(std::forward<decltype(args)>(args)...);
-    });
+    return traits::unpack(
+        [](auto&&... args) {
+          return spread_this(std::forward<decltype(args)>(args)...);
+        },
+        unpack_lazy(std::move(args_)));
   }
 };
 
@@ -208,8 +210,8 @@ template <typename... Args, typename Callback, typename Data>
 constexpr auto finalize_impl(traits::identity<std::tuple<Args...>>,
                              Callback&& callback, Data&& data) {
   // Call the final callback with the cleaned result
-  return traits::unpack(unbox_continuables(std::forward<Data>(data)),
-                        std::forward<Callback>(callback));
+  return traits::unpack(std::forward<Callback>(callback),
+                       unbox_continuables(std::forward<Data>(data)));
 }
 
 struct hint_mapper {

include/continuable/detail/connection-seq.hpp

@@ -61,7 +61,7 @@ auto sequential_connect(Left&& left, Right&& right) {
     return std::move(right).then([previous = std::make_tuple(
                                       std::forward<decltype(args)>(args)...)](
         auto&&... args) mutable {
-      return traits::merge(
+      return std::tuple_cat(
           std::move(previous),
           std::make_tuple(std::forward<decltype(args)>(args)...));
     });

include/continuable/detail/connection.hpp

@@ -56,7 +56,7 @@ template <typename... LeftArgs, typename... RightArgs>
 auto chain_connection(std::tuple<LeftArgs...> leftPack,
                       std::tuple<RightArgs...> rightPack) {
 
-  return traits::merge(std::move(leftPack), std::move(rightPack));
+  return std::tuple_cat(std::move(leftPack), std::move(rightPack));
 }
 
 /// Normalizes a continuation to a tuple holding an arbitrary count of

include/continuable/detail/features.hpp

@@ -58,6 +58,8 @@
   #define CONTINUABLE_HAS_CXX17_VOID_T
 #else
   // Generic feature detection based on __has_feature
+  // and other preprocessor definitions based on:
+  // http://en.cppreference.com/w/User:D41D8CD98F/feature_testing_macros
   #if defined(__has_feature)
     #if !defined(CONTINUABLE_HAS_CXX17_CONSTEXPR_IF) &&                        \
         __has_feature(cxx_if_constexpr)

include/continuable/detail/promisify.hpp

@@ -77,14 +77,15 @@ struct promisify_helper {
         auto&& promise) mutable {
 
       traits::unpack(
-          std::move(args), [promise = std::forward<decltype(promise)>(promise)](
-                               auto&&... args) mutable {
+          [promise = std::forward<decltype(promise)>(promise)](
+              auto&&... args) mutable {
             Evaluator<std::decay_t<decltype(promise)>> evaluator{
                 std::move(promise)};
 
             util::invoke(std::forward<decltype(args)>(args)...,
                          std::move(evaluator));
-          });
+          },
+          std::move(args));
     });
   }
 };

include/continuable/detail/traits.hpp

@@ -32,7 +32,6 @@
 #define CONTINUABLE_DETAIL_TRAITS_HPP_INCLUDED
 
 #include <cstdint>
-#include <initializer_list>
 #include <tuple>
 #include <type_traits>
 #include <utility>
@@ -184,108 +183,33 @@ constexpr auto static_if(Type&& type, Check&& check,
                                 std::forward<FalseCallback>(falseCallback));
 }
 
-/// Calls the given unpacker with the content of the given sequence
-template <typename U, std::size_t... I>
-constexpr decltype(auto) unpack(std::integer_sequence<std::size_t, I...>,
-                                U&& unpacker) {
-  return std::forward<U>(unpacker)(std::integral_constant<std::size_t, I>{}...);
-}
-
+namespace detail {
 /// Calls the given unpacker with the content of the given sequenceable
-template <typename F, typename U, std::size_t... I>
-constexpr auto unpack(F&& first_sequenceable, U&& unpacker,
-                      std::integer_sequence<std::size_t, I...>)
+template <typename U, typename F, std::size_t... I>
+constexpr auto unpack_impl(U&& unpacker, F&& first_sequenceable,
+                           std::integer_sequence<std::size_t, I...>)
     -> decltype(std::forward<U>(unpacker)(
-        get<I>(std::forward<F>(first_sequenceable))...)) {
+        std::get<I>(std::forward<F>(first_sequenceable))...)) {
   (void)first_sequenceable;
   return std::forward<U>(unpacker)(
-      get<I>(std::forward<F>(first_sequenceable))...);
-}
-/// Calls the given unpacker with the content of the given sequenceable
-template <typename F, typename S, typename U, std::size_t... If,
-          std::size_t... Is>
-constexpr auto unpack(F&& first_sequenceable, S&& second_sequenceable,
-                      U&& unpacker, std::integer_sequence<std::size_t, If...>,
-                      std::integer_sequence<std::size_t, Is...>)
-    -> decltype(std::forward<U>(unpacker)(
-        get<If>(std::forward<F>(first_sequenceable))...,
-        get<Is>(std::forward<S>(second_sequenceable))...)) {
-  (void)first_sequenceable;
-  (void)second_sequenceable;
-  return std::forward<U>(unpacker)(
-      get<If>(std::forward<F>(first_sequenceable))...,
-      get<Is>(std::forward<S>(second_sequenceable))...);
-}
-/// Calls the given unpacker with the content of the given sequenceable
-template <typename F, typename U>
-constexpr auto unpack(F&& first_sequenceable, U&& unpacker)
-    -> decltype(unpack(std::forward<F>(first_sequenceable),
-                       std::forward<U>(unpacker),
-                       sequence_of(identify<decltype(first_sequenceable)>{}))) {
-  return unpack(std::forward<F>(first_sequenceable), std::forward<U>(unpacker),
-                sequence_of(identify<decltype(first_sequenceable)>{}));
-}
-/// Calls the given unpacker with the content of the given sequenceables
-template <typename F, typename S, typename U>
-constexpr auto unpack(F&& first_sequenceable, S&& second_sequenceable,
-                      U&& unpacker)
-    -> decltype(unpack(std::forward<F>(first_sequenceable),
-                       std::forward<S>(second_sequenceable),
-                       std::forward<U>(unpacker),
-                       sequence_of(identity_of(first_sequenceable)),
-                       sequence_of(identity_of(second_sequenceable)))) {
-  return unpack(std::forward<F>(first_sequenceable),
-                std::forward<S>(second_sequenceable), std::forward<U>(unpacker),
-                sequence_of(identity_of(first_sequenceable)),
-                sequence_of(identity_of(second_sequenceable)));
+      std::get<I>(std::forward<F>(first_sequenceable))...);
 }
+} // namespace detail
 
-/// Adds the given type at the back of the left sequenceable
-template <typename Left, typename Element>
-constexpr auto push(Left&& left, Element&& element) {
-  return unpack(std::forward<Left>(left), [&](auto&&... args) {
-    return std::make_tuple(std::forward<decltype(args)>(args)...,
-                           std::forward<Element>(element));
-  });
-}
+/// Calls the given callable object with the content of the given sequenceable
+///
+/// \note We can't use std::apply here since this implementation is SFINAE
+///       aware and the std version not! This would lead to compilation errors.
+template <typename Callable, typename TupleLike,
+          typename Sequence = std::make_index_sequence<
+              std::tuple_size<std::decay_t<TupleLike>>::value>>
+constexpr auto unpack(Callable&& obj, TupleLike&& tuple_like)
+    -> decltype(detail::unpack_impl(std::forward<Callable>(obj),
+                                    std::forward<TupleLike>(tuple_like),
+                                    Sequence{})) {
 
-/// Adds the element to the back of the identity
-template <typename... Args, typename Element>
-constexpr auto push(identity<Args...>, identity<Element>) noexcept {
-  return identity<Args..., Element>{};
-}
-
-/// Removes the first element from the identity
-template <typename First, typename... Rest>
-constexpr auto pop_first(identity<First, Rest...>) noexcept {
-  return identity<Rest...>{};
-}
-
-/// Returns the merged sequence
-template <typename Left>
-constexpr auto merge(Left&& left) {
-  return std::forward<Left>(left);
-}
-/// Merges the left sequenceable with the right ones
-template <typename Left, typename Right, typename... Rest>
-constexpr auto merge(Left&& left, Right&& right, Rest&&... rest) {
-  // Merge the left with the right sequenceable and
-  // merge the result with the rest.
-  return merge(unpack(std::forward<Left>(left), std::forward<Right>(right),
-                      [&](auto&&... args) {
-                        // Maybe use: template <template<typename...> class T,
-                        // typename... Args>
-                        return std::make_tuple(
-                            std::forward<decltype(args)>(args)...);
-                      }),
-               std::forward<Rest>(rest)...);
-}
-/// Merges the left identity with the right ones
-template <typename... LeftArgs, typename... RightArgs, typename... Rest>
-constexpr auto merge(identity<LeftArgs...> /*left*/,
-                     identity<RightArgs...> /*right*/, Rest&&... rest) {
-  return merge(identity<LeftArgs..., RightArgs...>{},
-               std::forward<Rest>(rest)...);
+  return detail::unpack_impl(std::forward<Callable>(obj),
+                             std::forward<TupleLike>(tuple_like), Sequence{});
 }
 
 namespace detail {

include/continuable/detail/traverse-async.hpp

@@ -520,7 +520,7 @@ struct resume_state_callable {
 template <typename Frame, typename State>
 void resume_traversal_callable<Frame, State>::operator()() {
   auto hierarchy = std::tuple_cat(std::make_tuple(frame_), state_);
-  traits::unpack(std::move(hierarchy), resume_state_callable{});
+  traits::unpack(resume_state_callable{}, std::move(hierarchy));
 }
 
 /// Gives access to types related to the traversal frame

include/continuable/detail/traverse.hpp

@@ -192,10 +192,10 @@ struct flat_arraylizer {
 template <typename C, typename... T>
 constexpr auto apply_spread_impl(std::true_type, C&& callable, T&&... args)
     -> decltype(
-        traits::unpack(std::tuple_cat(undecorate(std::forward<T>(args))...),
-                       std::forward<C>(callable))) {
-  return traits::unpack(std::tuple_cat(undecorate(std::forward<T>(args))...),
-                        std::forward<C>(callable));
+        traits::unpack(std::forward<C>(callable),
+                      std::tuple_cat(undecorate(std::forward<T>(args))...))) {
+  return traits::unpack(std::forward<C>(callable),
+                       std::tuple_cat(undecorate(std::forward<T>(args))...));
 }
 
 /// Use the linear instantiation for variadic packs which don't
@@ -630,14 +630,14 @@ struct tuple_like_remapper<
 /// different types.
 template <typename Strategy, typename T, typename M>
 auto remap(Strategy, T&& container, M&& mapper) -> decltype(traits::unpack(
-    std::forward<T>(container),
     std::declval<tuple_like_remapper<Strategy, typename std::decay<M>::type,
-                                     typename std::decay<T>::type>>())) {
+                                     typename std::decay<T>::type>>(),
+    std::forward<T>(container))) {
   return traits::unpack(
-      std::forward<T>(container),
       tuple_like_remapper<Strategy, typename std::decay<M>::type,
                           typename std::decay<T>::type>{
-          std::forward<M>(mapper)});
+          std::forward<M>(mapper)},
+      std::forward<T>(container));
 }
 } // end namespace tuple_like_remapping
 

include/continuable/detail/util.hpp

@@ -49,27 +49,27 @@ constexpr void unused(T&&...) noexcept {
 }
 
 namespace detail {
+template <typename T, std::size_t... I>
+auto forward_except_last_impl(T&& tuple,
+                              std::integer_sequence<std::size_t, I...>) {
+  (void)tuple;
+  return std::forward_as_tuple(std::get<I>(std::forward<T>(tuple))...);
+}
+
 /// Forwards every element in the tuple except the last one
 template <typename T>
 auto forward_except_last(T&& sequenceable) {
   constexpr auto const size = pack_size_of(traits::identify<T>()) - 1U;
   constexpr auto const sequence = std::make_index_sequence<size>();
 
-  return traits::unpack(std::forward<T>(sequenceable),
-                        [](auto&&... args) {
-                          return std::forward_as_tuple(
-                              std::forward<decltype(args)>(args)...);
-                        },
-                        sequence);
+  return forward_except_last_impl(std::forward<T>(sequenceable), sequence);
 }
 
 /// We are able to call the callable with the arguments given in the tuple
 template <typename T, typename... Args>
 auto partial_invoke_impl(std::true_type, T&& callable,
                          std::tuple<Args...> args) {
-  return traits::unpack(std::move(args), [&](auto&&... arg) {
-    return std::forward<T>(callable)(std::forward<decltype(arg)>(arg)...);
-  });
+  return traits::unpack(std::forward<T>(callable), std::move(args));
 }
 
 /// We were unable to call the callable with the arguments in the tuple.

test/unit-test/multi/test-continuable-regression.cpp

@@ -33,21 +33,18 @@ using namespace cti::detail;
 TEST(regression_tests, are_multiple_args_mergeable) {
   {
     auto tp = std::make_tuple(1, 2, 3);
-    traits::merge(tp, tp, tp, tp, tp);
+    std::tuple_cat(tp, tp, tp, tp, tp);
   }
 
-  auto tp2 = traits::merge(std::make_tuple(), std::make_tuple(1),
-                           std::make_tuple(1, 2), std::make_tuple(1, 2, 3),
-                           std::make_tuple(1, 2, 3, 4));
+  auto tp2 = std::tuple_cat(std::make_tuple(), std::make_tuple(1),
+                            std::make_tuple(1, 2), std::make_tuple(1, 2, 3),
+                            std::make_tuple(1, 2, 3, 4));
 
-  auto count = traits::unpack(tp2, [](auto... args) {
-    std::vector<int> v{args...};
-    return std::accumulate(v.begin(), v.end(), 0);
-  });
+  auto count = traits::unpack(
+      [](auto... args) {
+        std::vector<int> v{args...};
+        return std::accumulate(v.begin(), v.end(), 0);
+      },
+      tp2);
   EXPECT_EQ(count, 20);
 }
-
-TEST(recursion_tests, are_noncopyable_mergeable) {
-  std::tuple<util::non_copyable> nc1, nc2, nc3;
-  traits::merge(std::move(nc1), std::move(nc2), std::move(nc3));
-}

test/unit-test/test-continuable.hpp

@@ -49,9 +49,11 @@ template <typename... Args>
 auto supplier_of(Args&&... args) {
   return [values = std::make_tuple(std::forward<Args>(args)...)](
       auto&& promise) mutable {
-    cti::detail::traits::unpack(std::move(values), [&](auto&&... passed) {
-      promise.set_value(std::forward<decltype(passed)>(passed)...);
-    });
+    cti::detail::traits::unpack(
+        [&](auto&&... passed) {
+          promise.set_value(std::forward<decltype(passed)>(passed)...);
+        },
+        std::move(values));
   };
 }