From d62eec2632a7c6fe88cfd5f7884a49d4df52cc3c Mon Sep 17 00:00:00 2001
From: Denis Blank <denis.blank@outlook.com>
Date: Sun, 18 Nov 2018 19:00:38 +0100
Subject: [PATCH] Started on transitioning to unref

---
 .../detail/traversal/traverse-async.hpp       | 27 +++++++-------
 .../continuable/detail/traversal/traverse.hpp | 37 +++++++++----------
 include/continuable/detail/utility/traits.hpp |  6 +++
 3 files changed, 36 insertions(+), 34 deletions(-)

diff --git a/include/continuable/detail/traversal/traverse-async.hpp b/include/continuable/detail/traversal/traverse-async.hpp
index bc67c43..9774810 100644
--- a/include/continuable/detail/traversal/traverse-async.hpp
+++ b/include/continuable/detail/traversal/traverse-async.hpp
@@ -97,10 +97,10 @@ public:
 /// given iterator tuple.
 template <typename Frame, typename State>
 auto make_resume_traversal_callable(Frame&& frame, State&& state)
-    -> resume_traversal_callable<typename std::decay<Frame>::type,
-                                 typename std::decay<State>::type> {
-  return resume_traversal_callable<typename std::decay<Frame>::type,
-                                   typename std::decay<State>::type>(
+    -> resume_traversal_callable<traits::unref_t<Frame>,
+                                 traits::unref_t<State>> {
+  return resume_traversal_callable<traits::unref_t<Frame>,
+                                   traits::unref_t<State>>(
       std::forward<Frame>(frame), std::forward<State>(state));
 }
 
@@ -292,8 +292,8 @@ struct dynamic_async_range {
 
 template <typename T>
 using dynamic_async_range_of_t = dynamic_async_range<
-    typename std::decay<decltype(std::begin(std::declval<T>()))>::type,
-    typename std::decay<decltype(std::end(std::declval<T>()))>::type>;
+    traits::unref_t<decltype(std::begin(std::declval<T>()))>,
+    traits::unref_t<decltype(std::end(std::declval<T>()))>>;
 
 /// Returns a dynamic range for the given type
 template <typename T>
@@ -337,9 +337,8 @@ public:
     auto hierarchy = std::tuple_cat(
         std::make_tuple(std::forward<Parent>(parent)), hierarchy_);
 
-    return async_traversal_point<Frame, typename std::decay<Parent>::type,
-                                 Hierarchy...>(frame_, std::move(hierarchy),
-                                               detached_);
+    return async_traversal_point<Frame, traits::unref_t<Parent>, Hierarchy...>(
+        frame_, std::move(hierarchy), detached_);
   }
 
   /// Forks the current traversal point and continues the child
@@ -405,7 +404,7 @@ public:
   /// Async traverse the current iterator
   template <typename Current>
   void async_traverse_one(Current&& current) {
-    using ElementType = typename std::decay<decltype(*current)>::type;
+    using ElementType = traits::unref_t<decltype(*current)>;
     return async_traverse_one_impl(container_category_of_t<ElementType>{},
                                    std::forward<Current>(current));
   }
@@ -453,8 +452,8 @@ public:
 /// given frame and hierarchy
 template <typename Frame, typename... Hierarchy>
 using traversal_point_of_t =
-    async_traversal_point<typename std::decay<Frame>::type,
-                          typename std::decay<Hierarchy>::type...>;
+    async_traversal_point<traits::unref_t<Frame>,
+                          traits::unref_t<Hierarchy>...>;
 
 /// A callable object which is capable of resuming an asynchronous
 /// pack traversal.
@@ -528,8 +527,8 @@ template <typename Visitor, typename... Args>
 struct async_traversal_types {
   /// Deduces to the async traversal frame type of the given
   /// traversal arguments and mapper
-  using frame_t = async_traversal_frame<typename std::decay<Visitor>::type,
-                                        typename std::decay<Args>::type...>;
+  using frame_t =
+      async_traversal_frame<traits::unref_t<Visitor>, traits::unref_t<Args>...>;
 
   /// The type of the demoted visitor type
   using visitor_t = Visitor;
diff --git a/include/continuable/detail/traversal/traverse.hpp b/include/continuable/detail/traversal/traverse.hpp
index e58dbb1..697ca4d 100644
--- a/include/continuable/detail/traversal/traverse.hpp
+++ b/include/continuable/detail/traversal/traverse.hpp
@@ -169,8 +169,7 @@ struct flat_arraylizer {
   /// Deduces to the array type when the array is instantiated
   /// with the given arguments.
   template <typename First, typename... Rest>
-  using array_type_of_t =
-      Type<typename std::decay<First>::type, 1 + sizeof...(Rest)>;
+  using array_type_of_t = Type<traits::unref_t<First>, 1 + sizeof...(Rest)>;
 
   // We overload with one argument here so Clang and GCC don't
   // have any issues with overloading against zero arguments.
@@ -408,8 +407,8 @@ using element_of_t = typename std::conditional<
 /// if the type is a l-value or r-value reference.
 template <typename T>
 using dereferenced_of_t =
-    typename std::conditional<std::is_reference<T>::value,
-                              typename std::decay<T>::type, T>::type;
+    typename std::conditional<std::is_reference<T>::value, traits::unref_t<T>,
+                              T>::type;
 
 /// Returns the type which is resulting if the mapping is applied to
 /// an element in the container.
@@ -423,8 +422,8 @@ using mapped_type_from_t = dereferenced_of_t<spreading::unpacked_of_t<decltype(
 
 /// Deduces to a true_type if the mapping maps to zero elements.
 template <typename T, typename M>
-using is_empty_mapped = spreading::is_empty_spread<typename std::decay<decltype(
-    std::declval<M>()(std::declval<element_of_t<T>>()))>::type>;
+using is_empty_mapped = spreading::is_empty_spread<traits::unref_t<decltype(
+    std::declval<M>()(std::declval<element_of_t<T>>()))>>;
 
 /// We are allowed to reuse the container if we map to the same
 /// type we are accepting and when we have
@@ -472,10 +471,9 @@ template <typename M, typename T>
 auto remap_container(container_mapping_tag<false, false>, M&& mapper,
                      T&& container)
     -> decltype(rebind_container<mapped_type_from_t<T, M>>(container)) {
-  static_assert(
-      has_push_back<typename std::decay<T>::type, element_of_t<T>>::value,
-      "Can only remap containers that provide a push_back "
-      "method!");
+  static_assert(has_push_back<traits::unref_t<T>, element_of_t<T>>::value,
+                "Can only remap containers that provide a push_back "
+                "method!");
 
   // Create the new container, which is capable of holding
   // the remappped types.
@@ -503,7 +501,7 @@ auto remap_container(container_mapping_tag<false, false>, M&& mapper,
 /// type we accepted such as int -> int.
 template <typename M, typename T>
 auto remap_container(container_mapping_tag<false, true>, M&& mapper,
-                     T&& container) -> typename std::decay<T>::type {
+                     T&& container) -> traits::unref_t<T> {
   for (auto&& val : container_accessor_of(std::forward<T>(container))) {
     val = spreading::unpack(
         std::forward<M>(mapper)(std::forward<decltype(val)>(val)));
@@ -629,12 +627,11 @@ struct tuple_like_remapper<
 /// different types.
 template <typename Strategy, typename T, typename M>
 auto remap(Strategy, T&& container, M&& mapper) -> decltype(traits::unpack(
-    std::declval<tuple_like_remapper<Strategy, typename std::decay<M>::type,
-                                     typename std::decay<T>::type>>(),
+    std::declval<tuple_like_remapper<Strategy, traits::unref_t<M>,
+                                     traits::unref_t<T>>>(),
     std::forward<T>(container))) {
   return traits::unpack(
-      tuple_like_remapper<Strategy, typename std::decay<M>::type,
-                          typename std::decay<T>::type>{
+      tuple_like_remapper<Strategy, traits::unref_t<M>, traits::unref_t<T>>{
           std::forward<M>(mapper)},
       std::forward<T>(container));
 }
@@ -645,7 +642,7 @@ auto remap(Strategy, T&& container, M&& mapper) -> decltype(traits::unpack(
 template <typename Strategy>
 struct mapping_strategy_base {
   template <typename T>
-  auto may_void(T&& element) const -> typename std::decay<T>::type {
+  auto may_void(T&& element) const -> traits::unref_t<T> {
     return std::forward<T>(element);
   }
 };
@@ -803,19 +800,19 @@ class mapping_helper : protected mapping_strategy_base<Strategy> {
   template <typename T>
   auto traverse(Strategy, T&& element)
       -> decltype(std::declval<mapping_helper>().match(
-          std::declval<container_category_of_t<typename std::decay<T>::type>>(),
+          std::declval<container_category_of_t<traits::unref_t<T>>>(),
           std::declval<T>()));
 
   /// \copybrief traverse
   template <typename T>
   auto try_traverse(Strategy, T&& element)
       -> decltype(std::declval<mapping_helper>().try_match(
-          std::declval<container_category_of_t<typename std::decay<T>::type>>(),
+          std::declval<container_category_of_t<traits::unref_t<T>>>(),
           std::declval<T>())) {
     // We use tag dispatching here, to categorize the type T whether
     // it satisfies the container or tuple like requirements.
     // Then we can choose the underlying implementation accordingly.
-    return try_match(container_category_of_t<typename std::decay<T>::type>{},
+    return try_match(container_category_of_t<traits::unref_t<T>>{},
                      std::forward<T>(element));
   }
 
@@ -861,7 +858,7 @@ public:
 /// Traverses the given pack with the given mapper and strategy
 template <typename Strategy, typename Mapper, typename... T>
 decltype(auto) transform(Strategy strategy, Mapper&& mapper, T&&... pack) {
-  mapping_helper<Strategy, typename std::decay<Mapper>::type> helper(
+  mapping_helper<Strategy, traits::unref_t<Mapper>> helper(
       std::forward<Mapper>(mapper));
   return helper.init_traverse(strategy, std::forward<T>(pack)...);
 }
diff --git a/include/continuable/detail/utility/traits.hpp b/include/continuable/detail/utility/traits.hpp
index a9e2736..3150f37 100644
--- a/include/continuable/detail/utility/traits.hpp
+++ b/include/continuable/detail/utility/traits.hpp
@@ -40,6 +40,12 @@
 namespace cti {
 namespace detail {
 namespace traits {
+/// Removes all references and qualifiers from the given type T,
+/// since traits::unref_t has too much overhead through checking for
+/// function pointers and arrays.
+template <typename T>
+using unref_t = std::remove_cv_t<std::remove_reference_t<T>>;
+
 namespace detail {
 template <typename T, typename... Args>
 struct index_of_impl;