From cd6f7445f0436a1dc0ee9a4b5dfe7861e7c08ab4 Mon Sep 17 00:00:00 2001
From: Denis Blank <denis.blank@outlook.com>
Date: Mon, 12 Mar 2018 08:25:44 +0100
Subject: [PATCH] Calculate the connection hint directly from the intermediate
 result

---
 .../detail/composition-aggregated.hpp         | 72 +++++--------------
 .../continuable/detail/composition-all.hpp    | 46 ++++++------
 .../continuable/detail/composition-any.hpp    | 31 ++++----
 .../continuable/detail/composition-seq.hpp    | 38 +++++-----
 include/continuable/detail/composition.hpp    | 17 +----
 5 files changed, 78 insertions(+), 126 deletions(-)

diff --git a/include/continuable/detail/composition-aggregated.hpp b/include/continuable/detail/composition-aggregated.hpp
index dc24ddc..a94dbe1 100644
--- a/include/continuable/detail/composition-aggregated.hpp
+++ b/include/continuable/detail/composition-aggregated.hpp
@@ -200,20 +200,28 @@ constexpr auto unbox_continuables(Args&&... args) {
 
 namespace detail {
 template <typename Callback, typename Data>
-void finalize_impl(traits::identity<void>, Callback&& callback, Data&&) {
-  std::forward<Callback>(callback)();
+constexpr auto finalize_impl(traits::identity<void>, Callback&& callback,
+                             Data&&) {
+  return std::forward<Callback>(callback)();
 }
 template <typename... Args, typename Callback, typename Data>
-void finalize_impl(traits::identity<std::tuple<Args...>>, Callback&& callback,
-                   Data&& data) {
+constexpr auto finalize_impl(traits::identity<std::tuple<Args...>>,
+                             Callback&& callback, Data&& data) {
   // Call the final callback with the cleaned result
-  traits::unpack(unbox_continuables(std::forward<Data>(data)),
-                 std::forward<Callback>(callback));
+  return traits::unpack(unbox_continuables(std::forward<Data>(data)),
+                        std::forward<Callback>(callback));
 }
+
+struct hint_mapper {
+  template <typename... T>
+  constexpr auto operator()(T...) -> hints::signature_hint_tag<T...> {
+    return {};
+  }
+};
 } // namespace detail
 
 template <typename Callback, typename Data>
-void finalize_data(Callback&& callback, Data&& data) {
+constexpr auto finalize_data(Callback&& callback, Data&& data) {
   using result_t = decltype(unbox_continuables(std::forward<Data>(data)));
   // Guard the final result against void
   return detail::finalize_impl(traits::identity<std::decay_t<result_t>>{},
@@ -221,54 +229,10 @@ void finalize_data(Callback&& callback, Data&& data) {
                                std::forward<Data>(data));
 }
 
-struct all_hint_deducer {
-  static constexpr auto deduce(hints::signature_hint_tag<>) noexcept {
-    return spread_this();
-  }
-
-  template <typename First>
-  static constexpr auto deduce(hints::signature_hint_tag<First>) {
-    return unpack_lazy(lazy_value_t<First>{});
-  }
-
-  template <typename First, typename Second, typename... Args>
-  static constexpr auto
-  deduce(hints::signature_hint_tag<First, Second, Args...>) {
-    return spread_this(unpack_lazy(lazy_value_t<First>{}),
-                       unpack_lazy(lazy_value_t<Second>{}),
-                       unpack_lazy(lazy_value_t<Args>{})...);
-  }
-
-  template <
-      typename T,
-      std::enable_if_t<base::is_continuable<std::decay_t<T>>::value>* = nullptr>
-  auto operator()(T&& /*continuable*/) const {
-    return deduce(hints::hint_of(traits::identify<T>{}));
-  }
-};
-
-constexpr auto deduce_from_pack(traits::identity<void>)
-    -> hints::signature_hint_tag<>;
-template <typename... T>
-constexpr auto deduce_from_pack(traits::identity<std::tuple<T...>>)
-    -> hints::signature_hint_tag<T...>;
-template <typename T>
-constexpr auto deduce_from_pack(traits::identity<T>)
-    -> hints::signature_hint_tag<T>;
-
-// We must guard the mapped type against to be void since this represents an
-// empty signature hint.
-template <typename Composition>
-constexpr auto deduce_hint(Composition&& /*composition*/) {
-  // Don't change this way since it addresses a GCC compiler bug:
-  // error: extra ';' [-Werror=pedantic]
-  //  std::declval<Composition>()))>{})){};
-  using mapped_t =
-      decltype(map_pack(all_hint_deducer{}, std::declval<Composition>()));
-  using deduced_t = decltype(deduce_from_pack(traits::identity<mapped_t>{}));
-  return deduced_t{};
+template <typename Data>
+constexpr auto hint_of_data() {
+  return decltype(finalize_data(detail::hint_mapper{}, std::declval<Data>())){};
 }
-
 } // namespace aggregated
 } // namespace composition
 } // namespace detail
diff --git a/include/continuable/detail/composition-all.hpp b/include/continuable/detail/composition-all.hpp
index 3159411..2c570c6 100644
--- a/include/continuable/detail/composition-all.hpp
+++ b/include/continuable/detail/composition-all.hpp
@@ -153,36 +153,36 @@ struct is_composition_strategy<composition_strategy_all_tag> // ...
 /// Finalizes the all logic of a given composition
 template <>
 struct composition_finalizer<composition_strategy_all_tag> {
-  template <typename Composition>
-  static constexpr auto hint() {
-    return decltype(aggregated::deduce_hint(std::declval<Composition>())){};
-  }
-
   /// Finalizes the all logic of a given composition
   template <typename Composition>
-  static auto finalize(Composition&& composition) {
-    return [composition = std::forward<Composition>(composition)] // ...
-        (auto&& callback) mutable {
+  static auto finalize(Composition&& composition, util::ownership ownership) {
+    // Create the target result from the composition
+    auto result =
+        aggregated::box_continuables(std::forward<Composition>(composition));
 
-      // Create the target result from the composition
-      auto result = aggregated::box_continuables(std::move(composition));
+    auto signature = aggregated::hint_of_data<decltype(result)>();
 
-      using submitter_t =
-          all::result_submitter<std::decay_t<decltype(callback)>,
-                                std::decay_t<decltype(result)>>;
+    return base::attorney::create(
+        [result = std::move(result)](auto&& callback) mutable {
 
-      // Create the shared state which holds the result and the final callback
-      auto state = std::make_shared<submitter_t>(
-          std::forward<decltype(callback)>(callback), std::move(result));
+          using submitter_t =
+              all::result_submitter<std::decay_t<decltype(callback)>,
+                                    std::decay_t<decltype(result)>>;
 
-      // Dispatch the continuables and store its partial result
-      // in the whole result
-      traverse_pack(all::continuable_dispatcher<submitter_t>{state},
-                    state->head());
+          // Create the shared state which holds the result and the final
+          // callback
+          auto state = std::make_shared<submitter_t>(
+              std::forward<decltype(callback)>(callback), std::move(result));
 
-      // Finalize the composition if all results arrived in-place
-      state->accept();
-    };
+          // Dispatch the continuables and store its partial result
+          // in the whole result
+          traverse_pack(all::continuable_dispatcher<submitter_t>{state},
+                        state->head());
+
+          // Finalize the composition if all results arrived in-place
+          state->accept();
+        },
+        signature, std::move(ownership));
   }
 };
 } // namespace composition
diff --git a/include/continuable/detail/composition-any.hpp b/include/continuable/detail/composition-any.hpp
index 0472e81..961346c 100644
--- a/include/continuable/detail/composition-any.hpp
+++ b/include/continuable/detail/composition-any.hpp
@@ -169,28 +169,27 @@ struct is_composition_strategy<composition_strategy_any_tag> // ...
 template <>
 struct composition_finalizer<composition_strategy_any_tag> {
   template <typename Composition>
-  static constexpr auto hint() {
-    return decltype(any::result_deducer::deduce(
+  static auto finalize(Composition&& composition, util::ownership ownership) {
+    auto signature = decltype(any::result_deducer::deduce(
         traversal::container_category_of_t<std::decay_t<Composition>>{},
         traits::identity<std::decay_t<Composition>>{})){};
-  }
 
-  template <typename Composition>
-  static auto finalize(Composition&& composition) {
-    return [composition = std::forward<Composition>(composition)](
-        auto&& callback) mutable {
+    return base::attorney::create(
+        [composition =
+             std::forward<Composition>(composition)](auto&& callback) mutable {
 
-      using submitter_t =
-          any::any_result_submitter<std::decay_t<decltype(callback)>>;
+          using submitter_t =
+              any::any_result_submitter<std::decay_t<decltype(callback)>>;
 
-      // Create the submitter which calls the given callback once at the
-      // first callback invocation.
-      auto submitter = std::make_shared<submitter_t>(
-          std::forward<decltype(callback)>(callback));
+          // Create the submitter which calls the given callback once at the
+          // first callback invocation.
+          auto submitter = std::make_shared<submitter_t>(
+              std::forward<decltype(callback)>(callback));
 
-      traverse_pack(any::continuable_dispatcher<submitter_t>{submitter},
-                    std::move(composition));
-    };
+          traverse_pack(any::continuable_dispatcher<submitter_t>{submitter},
+                        std::move(composition));
+        },
+        signature, std::move(ownership));
   }
 };
 } // namespace composition
diff --git a/include/continuable/detail/composition-seq.hpp b/include/continuable/detail/composition-seq.hpp
index a9cb60e..f3e782c 100644
--- a/include/continuable/detail/composition-seq.hpp
+++ b/include/continuable/detail/composition-seq.hpp
@@ -134,31 +134,31 @@ struct is_composition_strategy<composition_strategy_seq_tag> // ...
 /// Finalizes the seq logic of a given composition
 template <>
 struct composition_finalizer<composition_strategy_seq_tag> {
-  template <typename Composition>
-  static constexpr auto hint() {
-    return decltype(aggregated::deduce_hint(std::declval<Composition>())){};
-  }
-
   /// Finalizes the all logic of a given composition
   template <typename Composition>
-  static auto finalize(Composition&& composition) {
-    return [composition = std::forward<Composition>(composition)] // ...
-        (auto&& callback) mutable {
+  static auto finalize(Composition&& composition, util::ownership ownership) {
 
-      auto boxed = aggregated::box_continuables(std::move(composition));
+    auto result =
+        aggregated::box_continuables(std::forward<Composition>(composition));
 
-      // The data from which the visitor is constructed in-place
-      using data_t =
-          seq::sequential_dispatch_data<std::decay_t<decltype(callback)>,
-                                        std::decay_t<decltype(boxed)>>;
+    auto signature = aggregated::hint_of_data<decltype(result)>();
 
-      // The visitor type
-      using visitor_t = seq::sequential_dispatch_visitor<data_t>;
+    return base::attorney::create(
+        [result = std::move(result)](auto&& callback) mutable {
 
-      traverse_pack_async(
-          async_traverse_in_place_tag<visitor_t>{},
-          data_t{std::forward<decltype(callback)>(callback), std::move(boxed)});
-    };
+          // The data from which the visitor is constructed in-place
+          using data_t =
+              seq::sequential_dispatch_data<std::decay_t<decltype(callback)>,
+                                            std::decay_t<decltype(result)>>;
+
+          // The visitor type
+          using visitor_t = seq::sequential_dispatch_visitor<data_t>;
+
+          traverse_pack_async(async_traverse_in_place_tag<visitor_t>{},
+                              data_t{std::forward<decltype(callback)>(callback),
+                                     std::move(result)});
+        },
+        signature, std::move(ownership));
   }
 };
 } // namespace composition
diff --git a/include/continuable/detail/composition.hpp b/include/continuable/detail/composition.hpp
index 75adb14..eaabaf3 100644
--- a/include/continuable/detail/composition.hpp
+++ b/include/continuable/detail/composition.hpp
@@ -47,7 +47,7 @@ namespace detail {
 /// The namespace `composition` offers methods to chain continuations together
 /// with `all`, `any` or `seq` logic.
 namespace composition {
-  template <typename T>
+template <typename T>
 struct is_composition_strategy // ...
     : std::false_type {};
 
@@ -133,13 +133,8 @@ auto finalize_composition(continuable_base<Data, Strategy>&& continuation) {
   util::ownership ownership = base::attorney::ownership_of(continuation);
   auto composition = base::attorney::consume_data(std::move(continuation));
 
-  // Retrieve the new signature hint
-  constexpr auto const signature =
-      finalizer::template hint<decltype(composition)>();
-
   // Return a new continuable which
-  return base::attorney::create(finalizer::finalize(std::move(composition)),
-                                signature, std::move(ownership));
+  return finalizer::finalize(std::move(composition), std::move(ownership));
 }
 
 /// A base class from which the continuable may inherit in order to
@@ -203,13 +198,7 @@ auto apply_composition(Strategy, Args&&... args) {
   auto composition = map_pack(prepare_continuables{ownership},
                               std::make_tuple(std::forward<Args>(args)...));
 
-  // Retrieve the new signature hint
-  constexpr auto const signature =
-      finalizer::template hint<decltype(composition)>();
-
-  // Return a new continuable which
-  return base::attorney::create(finalizer::finalize(std::move(composition)),
-                                signature, std::move(ownership));
+  return finalizer::finalize(std::move(composition), std::move(ownership));
 }
 } // namespace composition
 } // namespace detail