Use new types instead of aliases for type erasures

* Makes compiler output much more readable
  This is configurateable through CONTINUABLE_WITH_IMMEDIATE_TYPES,
  and automatically enabled for debug builds but disabled
  for release builds.
* Remove the old continuable-trait.hpp header
* Make the signature of continuable not dependent anymore
  on any size of the arguments which fixes the compilation
  with forward declared types.
  Thanks Rogiel for the correspoding bug report.
  Closes #11

.travis.yml

@@ -20,6 +20,7 @@ matrix:
             - ninja-build
       env:
         - COMPILER=g++-6
+        - BUILD_CONFIG=Debug
         - WITH_NO_EXCEPTIONS=OFF
         - WITH_AWAIT=OFF
         - WITH_LIGHT_TESTS=ON
@@ -36,6 +37,7 @@ matrix:
             - ninja-build
       env:
         - COMPILER=clang++-5.0
+        - BUILD_CONFIG=Release
         - WITH_NO_EXCEPTIONS=OFF
         - WITH_AWAIT=OFF
         - WITH_LIGHT_TESTS=OFF
@@ -52,6 +54,7 @@ matrix:
             - ninja-build
       env:
         - COMPILER=clang++-5.0
+        - BUILD_CONFIG=Debug
         - WITH_NO_EXCEPTIONS=ON
         - WITH_AWAIT=ON
         - WITH_LIGHT_TESTS=ON

appveyor.yml

@@ -3,11 +3,14 @@ image:
 
 environment:
   matrix:
-    - WITH_NO_EXCEPTIONS: OFF
+    - CONFIGURATION: Debug
+      WITH_NO_EXCEPTIONS: OFF
       WITH_CPP_LATEST: OFF
-    - WITH_NO_EXCEPTIONS: ON
+    - CONFIGURATION: Debug
+      WITH_NO_EXCEPTIONS: ON
       WITH_CPP_LATEST: OFF
-    - WITH_NO_EXCEPTIONS: OFF
+    - CONFIGURATION: Release
+      WITH_NO_EXCEPTIONS: OFF
       WITH_CPP_LATEST: ON
 
 configuration:

doc/Doxyfile

@@ -38,13 +38,13 @@ PROJECT_NAME           = Continuable
 # could be handy for archiving the generated documentation or if some version
 # control system is used.
 
-PROJECT_NUMBER         = 3.0.0
+PROJECT_NUMBER         = 4.0.0
 
 # Using the PROJECT_BRIEF tag one can provide an optional one line description
 # for a project that appears at the top of each page and should give viewer a
 # quick idea about the purpose of the project. Keep the description short.
 
-PROJECT_BRIEF          = 
+PROJECT_BRIEF          = "C++14 asynchronous allocation aware futures"
 
 # With the PROJECT_LOGO tag one can specify a logo or an icon that is included
 # in the documentation. The maximum height of the logo should not exceed 55

doc/changelog.dox

@@ -41,7 +41,7 @@ New helper functions were added to create ready continuables:
 
 The implementation of connections were rewritten entirely.
 It is possible now to connect runtime sized containers as well as
-deeply nested sequences. See \ref tutorial-connections for details.
+deeply nested sequences. See \ref tutorial-connecting-continuables for details.
 
 Additionally connection overloads were added that accept two iterators
 in order to come closer to the interface of the standard library.

doc/configuration.dox

@@ -34,6 +34,7 @@ in order to change the libraries behaviour:
 | `CONTINUABLE_WITH_CUSTOM_ERROR_TYPE`      | Exceptions are disabled and the type defined by `CONTINUABLE_WITH_CUSTOM_ERROR_TYPE` is used as \ref error_type . See \ref tutorial-chaining-continuables-fail for details. |
 | `CONTINUABLE_WITH_UNHANDLED_EXCEPTIONS`   | Allows unhandled exceptions in asynchronous call hierarchies. See \ref tutorial-chaining-continuables-fail for details. |
 | `CONTINUABLE_WITH_CUSTOM_FINAL_CALLBACK`  | Allows to customize the final callback which can be used to implement custom unhandled asynchronous exception handlers. |
+| `CONTINUABLE_WITH_IMMEDIATE_TYPES`        | Don't decorate the used type erasure, which is done to keep type names minimal for better error messages in debug builds. |
 | `CONTINUABLE_WITH_EXPERIMENTAL_COROUTINE` | Enables support for experimental coroutines and `co_await` expressions. See \ref continuable_base::operator co_await() for details. |
 
 */

include/continuable/continuable-base.hpp

@@ -123,19 +123,31 @@ public:
             std::enable_if_t<detail::base::can_accept_continuation<
                 Data, Annotation,
                 detail::traits::unrefcv_t<OtherData>>::value>* = nullptr>
-  continuable_base(OtherData&& data)
+  /* implicit */ continuable_base(OtherData&& data)
       : data_(detail::base::proxy_continuable<
               Annotation, detail::traits::unrefcv_t<OtherData>>(
             std::forward<OtherData>(data))) {
   }
 
+  /// Constructor taking the data of other continuable_base objects
+  /// while erasing the hint.
+  ///
+  /// This constructor makes it possible to replace the internal data object of
+  /// the continuable by any object which is useful for type-erasure.
+  /*template <typename OData,
+            std::enable_if_t<std::is_convertible<
+                detail::traits::unrefcv_t<OData>, Data>::value>* = nullptr>
+continuable_base(continuable_base<OData, Annotation>&& other)
+      : continuable_base(std::move(other).consume()) {
+  }*/
+
   /// Constructor taking the data of other continuable_base objects
   /// while erasing the hint.
   ///
   /// This constructor makes it possible to replace the internal data object of
   /// the continuable by any object which is useful for type-erasure.
   template <typename OData, typename OAnnotation>
-  continuable_base(continuable_base<OData, OAnnotation>&& other)
+  /* implicit */ continuable_base(continuable_base<OData, OAnnotation>&& other)
       : continuable_base(std::move(other).finish().consume()) {
   }
 
@@ -853,7 +865,7 @@ constexpr auto make_continuable(Continuation&& continuation) {
 template <typename... Args>
 auto make_ready_continuable(Args&&... args) {
   using detail::base::ready_continuation;
-  using detail::traits::identity;
+  using detail::identity;
   using detail::traits::unrefcv_t;
   return detail::base::attorney::create_from_raw(
       ready_continuation<unrefcv_t<Args>...>{std::forward<Args>(args)...},
@@ -932,7 +944,7 @@ auto make_cancelling_continuable() {
 ///     // Recovered from the failure
 ///   })
 /// ```
-/// A corresponding \ref result is returned by \ref recover:
+/// A corresponding \ref result is returned by \ref recover
 /// ```cpp
 /// http_request("example.com")
 ///   .then([](std::string content) -> cti::result<int, int> {

include/continuable/continuable-coroutine.hpp

@@ -51,7 +51,7 @@ namespace std {
 namespace experimental {
 template <typename Data, typename... Args, typename... FunctionArgs>
 struct coroutine_traits<
-    cti::continuable_base<Data, cti::detail::traits::identity<Args...>>,
+    cti::continuable_base<Data, cti::detail::identity<Args...>>,
     FunctionArgs...> {
 
   using promise_type =

include/continuable/continuable-primitives.hpp

@@ -32,6 +32,7 @@
 #define CONTINUABLE_PRIMITIVES_HPP_INCLUDED
 
 #include <continuable/detail/core/types.hpp>
+#include <continuable/detail/utility/identity.hpp>
 
 namespace cti {
 /// \defgroup Primitives Primitives
@@ -50,12 +51,19 @@ namespace cti {
 /// ```cpp
 /// template<typename... Args>
 /// struct callback {
-///   void operator() (Args...);
+///   void operator() (Args...) &&;
-///   void operator() (cti::exception_arg_t, cti::exception_t);
+///   void operator() (cti::exception_arg_t, cti::exception_t) &&;
 /// };
 /// ```
 /// \{
 
+/// Represents the tag type that is used to specify the signature hint
+/// of a continuable_base or promise_base.
+///
+/// \since 4.0.0
+template <typename... Args>
+using signature_arg_t = detail::identity<Args...>;
+
 /// Represents the tag type that is used to query the continuation
 /// for whether it resolves the callback instantly with its arguments
 /// without having side effects.
@@ -69,7 +77,7 @@ struct is_ready_arg_t {};
 /// It's required that the query of is_ready_arg_t returns true.
 ///
 /// \since 4.0.0
-struct query_arg_t {};
+struct query_arg_t { };
 
 /// Represents the tag type that is used to disambiguate the
 /// callback operator() in order to take the exception asynchronous chain.
@@ -87,7 +95,7 @@ struct exception_arg_t {};
 ///
 [[deprecated("The dispatch_error_tag was replaced by exception_arg_t and will "
              "be removed in a later major version!")]] //
-typedef exception_arg_t dispatch_error_tag;
+    typedef exception_arg_t dispatch_error_tag;
 
 /// Represents the type that is used as exception type
 ///
@@ -108,7 +116,7 @@ using exception_t = detail::types::exception_t;
 ///
 [[deprecated("The error_type was replaced by exception_t and will "
              "be removed in a later major version!")]] //
-typedef exception_t error_type;
+    typedef exception_t error_type;
 /// \}
 } // namespace cti
 

include/continuable/continuable-promise-base.hpp

@@ -36,6 +36,7 @@
 #include <continuable/continuable-primitives.hpp>
 #include <continuable/detail/core/annotation.hpp>
 #include <continuable/detail/core/types.hpp>
+#include <continuable/detail/utility/traits.hpp>
 #include <continuable/detail/utility/util.hpp>
 
 namespace cti {
@@ -62,7 +63,7 @@ class promise_base
   /// \cond false
   ;
 template <typename Data, typename... Args>
-class promise_base<Data, detail::traits::identity<Args...>>
+class promise_base<Data, detail::identity<Args...>>
     : detail::util::non_copyable
   /// \endcond
 { // clang-format on
@@ -83,8 +84,9 @@ public:
   /// \endcond
 
   /// Constructor accepting any object convertible to the data object
-  template <typename OData, std::enable_if_t<std::is_convertible<
+  template <typename OData,
-                                std::decay_t<OData>, Data>::value>* = nullptr>
+            std::enable_if_t<std::is_convertible<
+                detail::traits::unrefcv_t<OData>, Data>::value>* = nullptr>
   promise_base(OData&& data) : data_(std::forward<OData>(data)) {
   }
 

include/continuable/continuable-testing.hpp

@@ -158,7 +158,7 @@
 /// \since 1.0.0
 #define ASSERT_ASYNC_TYPES(CONTINUABLE, ...)                                   \
   cti::detail::testing::assert_async_types(                                    \
-      CONTINUABLE, cti::detail::traits::identity<__VA_ARGS__>{})
+      CONTINUABLE, cti::detail::identity<__VA_ARGS__>{})
 
 /// Asserts that the continuable is finished with the given exception
 ///

include/continuable/continuable-trait.hpp

@@ -1,89 +0,0 @@
-
-/*
-
-                        /~` _  _ _|_. _     _ |_ | _
-                        \_,(_)| | | || ||_|(_||_)|(/_
-
-                    https://github.com/Naios/continuable
-                                   v4.0.0
-
-  Copyright(c) 2015 - 2018 Denis Blank <denis.blank at outlook dot com>
-
-  Permission is hereby granted, free of charge, to any person obtaining a copy
-  of this software and associated documentation files(the "Software"), to deal
-  in the Software without restriction, including without limitation the rights
-  to use, copy, modify, merge, publish, distribute, sublicense, and / or sell
-  copies of the Software, and to permit persons to whom the Software is
-  furnished to do so, subject to the following conditions :
-
-  The above copyright notice and this permission notice shall be included in
-  all copies or substantial portions of the Software.
-
-  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
-  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
-  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.IN NO EVENT SHALL THE
-  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
-  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
-  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
-  SOFTWARE.
-**/
-
-#ifndef CONTINUABLE_TRAIT_HPP_INCLUDED
-#define CONTINUABLE_TRAIT_HPP_INCLUDED
-
-#include <cstddef>
-#include <tuple>
-#include <continuable/continuable-base.hpp>
-#include <continuable/continuable-primitives.hpp>
-#include <continuable/continuable-promise-base.hpp>
-#include <continuable/detail/core/annotation.hpp>
-#include <continuable/detail/core/types.hpp>
-
-namespace cti {
-/// \defgroup Types Types
-/// provides the \link cti::continuable continuable\endlink and \link
-/// cti::promise promise\endlink facility for type erasure.
-/// \{
-
-/// Trait to retrieve a continuable_base type with a given type-erasure backend.
-///
-/// Every object may me used as type-erasure backend as long as the
-/// requirements of a `std::function` like wrapper are satisfied.
-///
-/// \tparam CallbackWrapper The type which is used to erase the callback.
-///
-/// \tparam ContinuationWrapper The type which is used to erase the
-///         continuation data.
-///
-/// \tparam Args The current signature of the continuable.
-template <template <std::size_t, typename...> class CallbackWrapper,
-          template <std::size_t, typename...> class ContinuationWrapper,
-          typename... Args>
-class continuable_trait {
-
-  using callback = CallbackWrapper<0U, void(Args...)&&,
-                                   void(exception_arg_t, exception_t) &&>;
-
-public:
-  /// The promise type which is used to resolve continuations
-  using promise = promise_base<callback, detail::traits::identity<Args...>>;
-
-  /// The continuable type for the given parameters.
-  using continuable = continuable_base<
-      ContinuationWrapper<
-          // Size the buffer for the small functor optimization so the
-          // result itself fits in and guarantee that a pointer can
-          // fit in as well.
-          (sizeof(detail::base::ready_continuation<Args...>) < sizeof(void*)
-               ? sizeof(void*)
-               : sizeof(detail::base::ready_continuation<Args...>)),
-          void(promise),                   //
-          bool(is_ready_arg_t) const,      //
-          std::tuple<Args...>(query_arg_t) //
-          >,
-      detail::traits::identity<Args...>>;
-};
-/// \}
-} // namespace cti
-
-#endif // CONTINUABLE_TRAIT_HPP_INCLUDED

include/continuable/continuable-types.hpp

@@ -31,9 +31,11 @@
 #ifndef CONTINUABLE_TYPES_HPP_INCLUDED
 #define CONTINUABLE_TYPES_HPP_INCLUDED
 
-#include <cstddef>
 #include <function2/function2.hpp>
-#include <continuable/continuable-trait.hpp>
+#include <continuable/continuable-base.hpp>
+#include <continuable/continuable-primitives.hpp>
+#include <continuable/continuable-promise-base.hpp>
+#include <continuable/detail/other/erasure.hpp>
 
 namespace cti {
 /// \defgroup Types Types
@@ -41,57 +43,65 @@ namespace cti {
 /// cti::promise promise\endlink facility for type erasure.
 /// \{
 
-// clang-format off
+/// Deduces to the preferred continuation capacity for a possible
-namespace detail {
+/// small functor optimization. The given capacity size is always enough to
-/// A function which isn't size adjusted and move only
+/// to avoid any allocation when storing a ready continuable_base.
-template<std::size_t, typename... Args>
+///
-using unique_function_adapter = fu2::unique_function<Args...>;
+/// \since 4.0.0
-/// A function which is size adjusted and move only
+template <typename... Args>
-template<std::size_t Size, typename... Args>
+using continuation_capacity = detail::erasure::continuation_capacity<Args...>;
-using unique_function_adjustable = fu2::function_base<true, false, Size,
-                                                      true, false, Args...>;
-
-/// We adjust the internal capacity of the outer function wrapper so
-/// we don't have to allocate twice when using `continuable<...>`.
-template<typename... Args>
-using unique_trait_of = continuable_trait<
-  unique_function_adapter,
-  unique_function_adjustable,
-  Args...
->;
-
-/// A type erasure for work objects
-using work = fu2::unique_function<void()>;
-} // namespace detail
 
 /// Defines a non-copyable continuation type which uses the
 /// function2 backend for type erasure.
 ///
 /// Usable like: `continuable<int, float>`
+///
+/// \note You can always define your own continuable with a type erasure of
+///       choice, the type erasure wrapper just needs to accept a
+///       callable object with a continuation signature as specified
+///       in the Primitives section.
+///
+/// \since 1.0.0
 template <typename... Args>
-using continuable = typename detail::unique_trait_of<
+using continuable = continuable_base<detail::erasure::continuation<Args...>, //
-  Args...
+                                     signature_arg_t<Args...>>;
->::continuable;
 
 /// Defines a non-copyable promise type which is using the
 /// function2 backend for type erasure.
 ///
 /// Usable like: `promise<int, float>`
+///
+/// \note You can always define your own promise with a type erasure of
+///       choice, the type erasure wrapper just needs to accept a
+///       callable object with a callback signature as specified
+///       in the Primitives section.
+///
+/// \since 1.0.0
 template <typename... Args>
-using promise = typename detail::unique_trait_of<
+using promise = promise_base<detail::erasure::callback<Args...>, //
-  Args...
+                             signature_arg_t<Args...>>;
->::promise;
 
 /// Defines a non-copyable type erasure which is capable of carrying
 /// callable objects passed to executors.
 ///
+/// \note You can always define your own work with a type erasure of
+///       choice, the type erasure wrapper just needs to accept a
+///       callable object which is callable with a `void()` signature.
+///
 /// \since 4.0.0
-using work = detail::work;
+class work : public fu2::unique_function<void()> {
+public:
+  work() = default;
+  ~work() = default;
+  work(work const&) = delete;
+  work(work&&) = default;
+  work& operator=(work const&) = delete;
+  work& operator=(work&&) = default;
 
-// TODO channel
+  using fu2::unique_function<void()>::unique_function;
-// TODO sink
+  using fu2::unique_function<void()>::operator=;
-
+  using fu2::unique_function<void()>::operator();
-// clang-format on
+};
 /// \}
 } // namespace cti
 

include/continuable/continuable.hpp

@@ -52,7 +52,6 @@ namespace cti {}
 #include <continuable/continuable-promise-base.hpp>
 #include <continuable/continuable-promisify.hpp>
 #include <continuable/continuable-result.hpp>
-#include <continuable/continuable-trait.hpp>
 #include <continuable/continuable-transforms.hpp>
 #include <continuable/continuable-traverse-async.hpp>
 #include <continuable/continuable-traverse.hpp>

include/continuable/detail/connection/connection-aggregated.hpp

@@ -75,13 +75,13 @@ T&& unpack_lazy(container::flat_variant<T>&& value) {
 template <typename Continuable>
 class continuable_box;
 template <typename Data>
-class continuable_box<continuable_base<Data, traits::identity<>>> {
+class continuable_box<continuable_base<Data, identity<>>> {
 
-  continuable_base<Data, traits::identity<>> continuable_;
+  continuable_base<Data, identity<>> continuable_;
 
 public:
   explicit continuable_box(
-      continuable_base<Data, traits::identity<>>&& continuable)
+      continuable_base<Data, identity<>>&& continuable)
       : continuable_(std::move(continuable)) {
   }
 
@@ -101,14 +101,14 @@ public:
   }
 };
 template <typename Data, typename First>
-class continuable_box<continuable_base<Data, traits::identity<First>>> {
+class continuable_box<continuable_base<Data, identity<First>>> {
 
-  continuable_base<Data, traits::identity<First>> continuable_;
+  continuable_base<Data, identity<First>> continuable_;
   lazy_value_t<First> first_;
 
 public:
   explicit continuable_box(
-      continuable_base<Data, traits::identity<First>>&& continuable)
+      continuable_base<Data, identity<First>>&& continuable)
       : continuable_(std::move(continuable)) {
   }
 
@@ -130,14 +130,14 @@ public:
 };
 template <typename Data, typename First, typename Second, typename... Rest>
 class continuable_box<
-    continuable_base<Data, traits::identity<First, Second, Rest...>>> {
+    continuable_base<Data, identity<First, Second, Rest...>>> {
 
-  continuable_base<Data, traits::identity<First, Second, Rest...>> continuable_;
+  continuable_base<Data, identity<First, Second, Rest...>> continuable_;
   lazy_value_t<std::tuple<First, Second, Rest...>> args_;
 
 public:
   explicit continuable_box(
-      continuable_base<Data, traits::identity<First, Second, Rest...>>&&
+      continuable_base<Data, identity<First, Second, Rest...>>&&
           continuable)
       : continuable_(std::move(continuable)) {
   }
@@ -209,12 +209,12 @@ constexpr auto unbox_continuables(Args&&... args) {
 
 namespace detail {
 template <typename Callback, typename Data>
-constexpr auto finalize_impl(traits::identity<void>, Callback&& callback,
+constexpr auto finalize_impl(identity<void>, Callback&& callback,
                              Data&&) {
   return std::forward<Callback>(callback)();
 }
 template <typename... Args, typename Callback, typename Data>
-constexpr auto finalize_impl(traits::identity<std::tuple<Args...>>,
+constexpr auto finalize_impl(identity<std::tuple<Args...>>,
                              Callback&& callback, Data&& data) {
   // Call the final callback with the cleaned result
   return traits::unpack(std::forward<Callback>(callback),
@@ -223,7 +223,7 @@ constexpr auto finalize_impl(traits::identity<std::tuple<Args...>>,
 
 struct hint_mapper {
   template <typename... T>
-  constexpr auto operator()(T...) -> traits::identity<T...> {
+  constexpr auto operator()(T...) -> identity<T...> {
     return {};
   }
 };
@@ -233,7 +233,7 @@ template <typename Callback, typename 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>>{},
+  return detail::finalize_impl(identity<std::decay_t<result_t>>{},
                                std::forward<Callback>(callback),
                                std::forward<Data>(data));
 }

include/continuable/detail/connection/connection-any.hpp

@@ -88,30 +88,30 @@ private:
 
 struct result_deducer {
   template <typename T>
-  static auto deduce_one(std::false_type, traits::identity<T>) {
+  static auto deduce_one(std::false_type, identity<T>) {
     static_assert(traits::fail<T>::value,
                   "Non continuable types except tuple like and homogeneous "
                   "containers aren't allowed inside an any expression!");
   }
   template <typename T>
-  static auto deduce_one(std::true_type, traits::identity<T> id) {
+  static auto deduce_one(std::true_type, identity<T> id) {
     return base::annotation_of(id);
   }
   template <typename T>
   static auto deduce(traversal::container_category_tag<false, false>,
-                     traits::identity<T> id) {
+                     identity<T> id) {
     return deduce_one<T>(base::is_continuable<T>{}, id);
   }
 
   /// Deduce a homogeneous container
   template <bool IsTupleLike, typename T>
   static auto deduce(traversal::container_category_tag<true, IsTupleLike>,
-                     traits::identity<T>) {
+                     identity<T>) {
 
     // Deduce the containing type
     using element_t = std::decay_t<decltype(*std::declval<T>().begin())>;
     return deduce(traversal::container_category_of_t<element_t>{},
-                  traits::identity<element_t>{});
+                  identity<element_t>{});
   }
 
   template <typename First, typename... T>
@@ -125,19 +125,19 @@ struct result_deducer {
 
   template <std::size_t... I, typename T>
   static auto deduce_tuple_like(std::integer_sequence<std::size_t, I...>,
-                                traits::identity<T>) {
+                                identity<T>) {
 
     return deduce_same_hints(deduce(
         traversal::container_category_of_t<
             std::decay_t<decltype(std::get<I>(std::declval<T>()))>>{},
-        traits::identity<
+        identity<
             std::decay_t<decltype(std::get<I>(std::declval<T>()))>>{})...);
   }
 
   /// Traverse tuple like container
   template <typename T>
   static auto deduce(traversal::container_category_tag<false, true>,
-                     traits::identity<T> id) {
+                     identity<T> id) {
 
     constexpr auto const size = std::tuple_size<T>::value;
     return deduce_tuple_like(std::make_index_sequence<size>{}, id);
@@ -172,7 +172,7 @@ struct connection_finalizer<connection_strategy_any_tag> {
   static auto finalize(Connection&& connection, util::ownership ownership) {
     constexpr auto const signature = decltype(any::result_deducer::deduce(
         traversal::container_category_of_t<std::decay_t<Connection>>{},
-        traits::identity<std::decay_t<Connection>>{})){};
+        identity<std::decay_t<Connection>>{})){};
 
     return base::attorney::create_from(
         [connection =

include/continuable/detail/core/annotation.hpp

@@ -42,7 +42,7 @@ struct annotation_trait;
 
 /// Specialization for a present signature hint
 template <typename... Args>
-struct annotation_trait<traits::identity<Args...>> {
+struct annotation_trait<identity<Args...>> {
   template <typename Continuable>
   static Continuable&& finish(Continuable&& continuable) {
     return std::forward<Continuable>(continuable);
@@ -55,9 +55,9 @@ namespace hints {
 ///
 /// This is the overload taking an arbitrary amount of args
 template <typename... HintArgs>
-struct from_args : std::common_type<traits::identity<HintArgs...>> {};
+struct from_args : std::common_type<identity<HintArgs...>> {};
 template <>
-struct from_args<void> : std::common_type<traits::identity<>> {};
+struct from_args<void> : std::common_type<identity<>> {};
 } // namespace hints
 } // namespace detail
 } // namespace cti

include/continuable/detail/core/base.hpp

@@ -122,8 +122,7 @@ struct ready_continuation<> {
 template <typename Hint, typename Continuation>
 struct proxy_continuable;
 template <typename... Args, typename Continuation>
-struct proxy_continuable<traits::identity<Args...>, Continuation>
+struct proxy_continuable<identity<Args...>, Continuation> : Continuation {
-    : Continuation {
 
   explicit proxy_continuable(Continuation continuation)
       : Continuation(std::move(continuation)) {
@@ -192,9 +191,9 @@ struct attorney {
 
 /// Returns the signature hint of the given continuable
 template <typename Data, typename... Args>
-constexpr traits::identity<Args...>
+constexpr identity<Args...>
-annotation_of(traits::identity<continuable_base<Data, //
+annotation_of(identity<continuable_base<Data, //
-                                                traits::identity<Args...>>>) {
+                                        identity<Args...>>>) {
   return {};
 }
 
@@ -275,30 +274,28 @@ constexpr void invoke_no_except(T&& callable, Args&&... args) noexcept {
 }
 
 template <typename... Args, typename T>
-void invoke_void_no_except(traits::identity<exception_arg_t, Args...>,
+void invoke_void_no_except(identity<exception_arg_t, Args...>,
                            T&& /*callable*/) noexcept {
   // Don't invoke the next failure handler when being in an exception handler
 }
 template <typename... Args, typename T>
-void invoke_void_no_except(traits::identity<Args...>, T&& callable) noexcept {
+void invoke_void_no_except(identity<Args...>, T&& callable) noexcept {
   std::forward<T>(callable)();
 }
 
 template <typename T, typename... Args>
-constexpr auto make_invoker(T&& invoke, traits::identity<Args...>) {
+constexpr auto make_invoker(T&& invoke, identity<Args...>) {
-  return invoker<std::decay_t<T>, traits::identity<Args...>>(
+  return invoker<std::decay_t<T>, identity<Args...>>(std::forward<T>(invoke));
-      std::forward<T>(invoke));
 }
 
 /// - continuable<?...> -> result(next_callback);
 template <typename Data, typename Annotation>
-constexpr auto
+constexpr auto invoker_of(identity<continuable_base<Data, Annotation>>) {
-invoker_of(traits::identity<continuable_base<Data, Annotation>>) {
   /// Get the hint of the unwrapped returned continuable
   using Type =
       decltype(std::declval<continuable_base<Data, Annotation>>().finish());
 
-  auto constexpr const hint = base::annotation_of(traits::identify<Type>{});
+  auto constexpr const hint = base::annotation_of(identify<Type>{});
 
   return make_invoker(
       [](auto&& callback, auto&& next_callback, auto&&... args) {
@@ -317,7 +314,7 @@ invoker_of(traits::identity<continuable_base<Data, Annotation>>) {
 
 /// - ? -> next_callback(?)
 template <typename T>
-constexpr auto invoker_of(traits::identity<T>) {
+constexpr auto invoker_of(identity<T>) {
   return make_invoker(
       [](auto&& callback, auto&& next_callback, auto&&... args) {
         CONTINUABLE_BLOCK_TRY_BEGIN
@@ -329,26 +326,26 @@ constexpr auto invoker_of(traits::identity<T>) {
                            std::move(result));
         CONTINUABLE_BLOCK_TRY_END
       },
-      traits::identify<T>{});
+      identify<T>{});
 }
 
 /// - void -> next_callback()
-inline auto invoker_of(traits::identity<void>) {
+inline auto invoker_of(identity<void>) {
   return make_invoker(
       [](auto&& callback, auto&& next_callback, auto&&... args) {
         CONTINUABLE_BLOCK_TRY_BEGIN
           invoke_callback(std::forward<decltype(callback)>(callback),
                           std::forward<decltype(args)>(args)...);
           invoke_void_no_except(
-              traits::identity<traits::unrefcv_t<decltype(args)>...>{},
+              identity<traits::unrefcv_t<decltype(args)>...>{},
               std::forward<decltype(next_callback)>(next_callback));
         CONTINUABLE_BLOCK_TRY_END
       },
-      traits::identity<>{});
+      identity<>{});
 }
 
 /// - empty_result -> <cancel>
-inline auto invoker_of(traits::identity<empty_result>) {
+inline auto invoker_of(identity<empty_result>) {
   return make_invoker(
       [](auto&& callback, auto&& next_callback, auto&&... args) {
         (void)next_callback;
@@ -362,11 +359,11 @@ inline auto invoker_of(traits::identity<empty_result>) {
           (void)result;
         CONTINUABLE_BLOCK_TRY_END
       },
-      traits::identity<>{});
+      identity<>{});
 }
 
 /// - exceptional_result -> <throw>
-inline auto invoker_of(traits::identity<exceptional_result>) {
+inline auto invoker_of(identity<exceptional_result>) {
   return make_invoker(
       [](auto&& callback, auto&& next_callback, auto&&... args) {
         util::unused(callback, next_callback, args...);
@@ -381,12 +378,12 @@ inline auto invoker_of(traits::identity<exceptional_result>) {
                            std::move(result).get_exception());
         CONTINUABLE_BLOCK_TRY_END
       },
-      traits::identity<>{});
+      identity<>{});
 }
 
 /// - result<?...> -> next_callback(?...)
 template <typename... Args>
-auto invoker_of(traits::identity<result<Args...>>) {
+auto invoker_of(identity<result<Args...>>) {
   return make_invoker(
       [](auto&& callback, auto&& next_callback, auto&&... args) {
         CONTINUABLE_BLOCK_TRY_BEGIN
@@ -416,7 +413,7 @@ auto invoker_of(traits::identity<result<Args...>>) {
         // asynchronous chain.
         CONTINUABLE_BLOCK_TRY_END
       },
-      traits::identity<Args...>{});
+      identity<Args...>{});
 }
 
 /// Returns a sequenced invoker which is able to invoke
@@ -443,15 +440,14 @@ inline auto sequenced_unpack_invoker() {
 
 // - std::pair<?, ?> -> next_callback(?, ?)
 template <typename First, typename Second>
-constexpr auto invoker_of(traits::identity<std::pair<First, Second>>) {
+constexpr auto invoker_of(identity<std::pair<First, Second>>) {
-  return make_invoker(sequenced_unpack_invoker(),
+  return make_invoker(sequenced_unpack_invoker(), identity<First, Second>{});
-                      traits::identity<First, Second>{});
 }
 
 // - std::tuple<?...>  -> next_callback(?...)
 template <typename... Args>
-constexpr auto invoker_of(traits::identity<std::tuple<Args...>>) {
+constexpr auto invoker_of(identity<std::tuple<Args...>>) {
-  return make_invoker(sequenced_unpack_invoker(), traits::identity<Args...>{});
+  return make_invoker(sequenced_unpack_invoker(), identity<Args...>{});
 }
 
 #undef CONTINUABLE_BLOCK_TRY_BEGIN
@@ -511,24 +507,20 @@ namespace proto {
 template <handle_results HandleResults, typename Base, typename Hint>
 struct result_handler_base;
 template <typename Base, typename... Args>
-struct result_handler_base<handle_results::no, Base,
+struct result_handler_base<handle_results::no, Base, identity<Args...>> {
-                           traits::identity<Args...>> {
   void operator()(Args... args) && {
     // Forward the arguments to the next callback
     std::move(static_cast<Base*>(this)->next_callback_)(std::move(args)...);
   }
 };
 template <typename Base, typename... Args>
-struct result_handler_base<handle_results::yes, Base,
+struct result_handler_base<handle_results::yes, Base, identity<Args...>> {
-                           traits::identity<Args...>> {
   /// The operator which is called when the result was provided
   void operator()(Args... args) && {
     // In order to retrieve the correct decorator we must know what the
     // result type is.
-    constexpr auto result =
+    constexpr auto result = identify<decltype(decoration::invoke_callback(
-        traits::identify<decltype(decoration::invoke_callback(
+        std::move(static_cast<Base*>(this)->callback_), std::move(args)...))>{};
-            std::move(static_cast<Base*>(this)->callback_),
-            std::move(args)...))>{};
 
     // Pick the correct invoker that handles decorating of the result
     auto invoker = decoration::invoker_of(result);
@@ -557,8 +549,7 @@ template <typename Base>
 struct error_handler_base<handle_errors::forward, Base> {
   /// The operator which is called when an error occurred
   void operator()(exception_arg_t, exception_t exception) && {
-    constexpr auto result =
+    constexpr auto result = identify<decltype(decoration::invoke_callback(
-        traits::identify<decltype(decoration::invoke_callback(
         std::move(static_cast<Base*>(this)->callback_), exception_arg_t{},
         std::move(exception)))>{};
 
@@ -582,16 +573,16 @@ struct callback_base;
 template <typename... Args, handle_results HandleResults,
           handle_errors HandleErrors, typename Callback, typename Executor,
           typename NextCallback>
-struct callback_base<traits::identity<Args...>, HandleResults, HandleErrors,
+struct callback_base<identity<Args...>, HandleResults, HandleErrors, Callback,
-                     Callback, Executor, NextCallback>
+                     Executor, NextCallback>
     : proto::result_handler_base<
           HandleResults,
-          callback_base<traits::identity<Args...>, HandleResults, HandleErrors,
+          callback_base<identity<Args...>, HandleResults, HandleErrors,
                         Callback, Executor, NextCallback>,
-          traits::identity<Args...>>,
+          identity<Args...>>,
       proto::error_handler_base<
           HandleErrors,
-          callback_base<traits::identity<Args...>, HandleResults, HandleErrors,
+          callback_base<identity<Args...>, HandleResults, HandleErrors,
                         Callback, Executor, NextCallback>>,
       util::non_copyable {
 
@@ -608,15 +599,15 @@ struct callback_base<traits::identity<Args...>, HandleResults, HandleErrors,
   /// Pull the result handling operator() in
   using proto::result_handler_base<
       HandleResults,
-      callback_base<traits::identity<Args...>, HandleResults, HandleErrors,
+      callback_base<identity<Args...>, HandleResults, HandleErrors, Callback,
-                    Callback, Executor, NextCallback>,
+                    Executor, NextCallback>,
-      traits::identity<Args...>>::operator();
+      identity<Args...>>::operator();
 
   /// Pull the error handling operator() in
   using proto::error_handler_base<
       HandleErrors,
-      callback_base<traits::identity<Args...>, HandleResults, HandleErrors,
+      callback_base<identity<Args...>, HandleResults, HandleErrors, Callback,
-                    Callback, Executor, NextCallback>>::operator();
+                    Executor, NextCallback>>::operator();
 
   /// Resolves the continuation with the given values
   void set_value(Args... args) {
@@ -683,21 +674,19 @@ struct final_callback : util::non_copyable {
 template <typename T, typename... Args>
 constexpr auto
 next_hint_of(std::integral_constant<handle_results, handle_results::yes>,
-             traits::identity<T> /*callback*/,
+             identity<T> /*callback*/, identity<Args...> /*current*/) {
-             traits::identity<Args...> /*current*/) {
   // Partial Invoke the given callback
   using Result = decltype(
       decoration::invoke_callback(std::declval<T>(), std::declval<Args>()...));
 
   // Return the hint of thr given invoker
-  return decltype(decoration::invoker_of(traits::identify<Result>{}).hint()){};
+  return decltype(decoration::invoker_of(identify<Result>{}).hint()){};
 }
 /// Don't progress the hint when we don't continue
 template <typename T, typename... Args>
 constexpr auto
 next_hint_of(std::integral_constant<handle_results, handle_results::no>,
-             traits::identity<T> /*callback*/,
+             identity<T> /*callback*/, identity<Args...> current) {
-             traits::identity<Args...> current) {
   return current;
 }
 
@@ -729,9 +718,9 @@ struct chained_continuation;
 template <typename... Args, typename... NextArgs, handle_results HandleResults,
           handle_errors HandleErrors, typename Continuation, typename Callback,
           typename Executor>
-struct chained_continuation<traits::identity<Args...>,
+struct chained_continuation<identity<Args...>, identity<NextArgs...>,
-                            traits::identity<NextArgs...>, HandleResults,
+                            HandleResults, HandleErrors, Continuation, Callback,
-                            HandleErrors, Continuation, Callback, Executor> {
+                            Executor> {
 
   Continuation continuation_;
   Callback callback_;
@@ -760,8 +749,8 @@ struct chained_continuation<traits::identity<Args...>,
     // - Continuation: continuation<[](auto&& callback) { callback("hi"); }>
     // - Callback: [](std::string) { }
     // - NextCallback: []() { }
-    auto proxy = callbacks::make_callback<traits::identity<Args...>,
+    auto proxy = callbacks::make_callback<identity<Args...>, HandleResults,
-                                          HandleResults, HandleErrors>(
+                                          HandleErrors>(
         std::move(callback_), std::move(executor_),
         std::forward<decltype(next_callback)>(next_callback));
 
@@ -791,9 +780,9 @@ struct chained_continuation<traits::identity<Args...>,
 // Specialization to unpack ready continuables directly
 template <typename... Args, typename... NextArgs, handle_results HandleResults,
           handle_errors HandleErrors, typename Callback, typename Executor>
-struct chained_continuation<
+struct chained_continuation<identity<Args...>, identity<NextArgs...>,
-    traits::identity<Args...>, traits::identity<NextArgs...>, HandleResults,
+                            HandleResults, HandleErrors,
-    HandleErrors, ready_continuation<Args...>, Callback, Executor> {
+                            ready_continuation<Args...>, Callback, Executor> {
 
   ready_continuation<Args...> continuation_;
   Callback callback_;
@@ -814,8 +803,8 @@ struct chained_continuation<
 
   template <typename NextCallback>
   void operator()(NextCallback&& next_callback) {
-    auto proxy = callbacks::make_callback<traits::identity<Args...>,
+    auto proxy = callbacks::make_callback<identity<Args...>, HandleResults,
-                                          HandleResults, HandleErrors>(
+                                          HandleErrors>(
         std::move(callback_), std::move(executor_),
         std::forward<decltype(next_callback)>(next_callback));
 
@@ -850,10 +839,10 @@ auto chain_continuation(Continuation&& continuation, Callback&& callback,
   static_assert(is_continuable<std::decay_t<Continuation>>{},
                 "Expected a continuation!");
 
-  using Hint = decltype(base::annotation_of(traits::identify<Continuation>()));
+  using Hint = decltype(base::annotation_of(identify<Continuation>()));
   constexpr auto next_hint =
       next_hint_of(std::integral_constant<handle_results, HandleResults>{},
-                   traits::identify<decltype(callback)>{}, Hint{});
+                   identify<decltype(callback)>{}, Hint{});
 
   auto ownership = attorney::ownership_of(continuation);
   auto data =
@@ -875,7 +864,7 @@ auto chain_continuation(Continuation&& continuation, Callback&& callback,
 /// - Continuation: continuation<[](auto&& callback) { callback("hi"); }>
 template <typename Data, typename... Args>
 void finalize_continuation(
-    continuable_base<Data, traits::identity<Args...>>&& continuation) noexcept {
+    continuable_base<Data, identity<Args...>>&& continuation) noexcept {
 #ifdef CONTINUABLE_WITH_CUSTOM_FINAL_CALLBACK
   invoke_continuation(std::move(continuation),
                       CONTINUABLE_WITH_CUSTOM_FINAL_CALLBACK<Args...>{});
@@ -890,13 +879,12 @@ void finalize_continuation(
 template <typename Data, typename Annotation, typename Continuation>
 struct can_accept_continuation : std::false_type {};
 template <typename Data, typename... Args, typename Continuation>
-struct can_accept_continuation<Data, traits::identity<Args...>, Continuation>
+struct can_accept_continuation<Data, identity<Args...>, Continuation>
     : traits::conjunction<
           traits::is_invocable<Continuation,
                                callbacks::final_callback<Args...>>,
           std::is_convertible<
-              proxy_continuable<traits::identity<Args...>, Continuation>,
+              proxy_continuable<identity<Args...>, Continuation>, Data>> {};
-              Data>> {};
 
 /// Workaround for GCC bug:
 /// https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64095

include/continuable/detail/core/types.hpp

@@ -33,6 +33,7 @@
 
 #include <utility>
 #include <continuable/detail/features.hpp>
+#include <continuable/detail/utility/identity.hpp>
 
 #ifndef CONTINUABLE_WITH_CUSTOM_ERROR_TYPE
 #ifndef CONTINUABLE_WITH_NO_EXCEPTIONS

include/continuable/detail/features.hpp

@@ -106,6 +106,18 @@
 #else
   #undef CONTINUABLE_HAS_EXCEPTIONS
 #endif
+
+/// Define CONTINUABLE_HAS_IMMEDIATE_TYPES when either
+/// - CONTINUABLE_WITH_IMMEDIATE_TYPES is defined
+/// - Building in release mode (NDEBUG is defined)
+///
+/// Build error messages will become more readable in debug mode while
+/// we don't suffer any runtime penalty in release.
+#if defined(CONTINUABLE_WITH_IMMEDIATE_TYPES) || defined(NDEBUG)
+  #define CONTINUABLE_HAS_IMMEDIATE_TYPES 1
+#else
+  #undef CONTINUABLE_HAS_IMMEDIATE_TYPES
+#endif
 // clang-format on
 
 #endif // CONTINUABLE_DETAIL_FEATURES_HPP_INCLUDED

include/continuable/detail/other/coroutines.hpp

@@ -57,7 +57,7 @@ using std::experimental::coroutine_handle;
 template <typename T>
 struct result_from_identity;
 template <typename... T>
-struct result_from_identity<traits::identity<T...>> {
+struct result_from_identity<identity<T...>> {
   using result_t = result<T...>;
 };
 
@@ -65,7 +65,7 @@ struct result_from_identity<traits::identity<T...>> {
 /// for waiting on a continuable in a stackless coroutine.
 template <typename Continuable>
 class awaitable {
-  using hint_t = decltype(base::annotation_of(traits::identify<Continuable>{}));
+  using hint_t = decltype(base::annotation_of(identify<Continuable>{}));
   using result_t = typename result_from_identity<hint_t>::result_t;
 
   /// The continuable which is invoked upon suspension

include/continuable/detail/other/erasure.hpp

@@ -0,0 +1,180 @@
+
+/*
+
+                        /~` _  _ _|_. _     _ |_ | _
+                        \_,(_)| | | || ||_|(_||_)|(/_
+
+                    https://github.com/Naios/continuable
+                                   v4.0.0
+
+  Copyright(c) 2015 - 2018 Denis Blank <denis.blank at outlook dot com>
+
+  Permission is hereby granted, free of charge, to any person obtaining a copy
+  of this software and associated documentation files(the "Software"), to deal
+  in the Software without restriction, including without limitation the rights
+  to use, copy, modify, merge, publish, distribute, sublicense, and / or sell
+  copies of the Software, and to permit persons to whom the Software is
+  furnished to do so, subject to the following conditions :
+
+  The above copyright notice and this permission notice shall be included in
+  all copies or substantial portions of the Software.
+
+  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.IN NO EVENT SHALL THE
+  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+  SOFTWARE.
+**/
+
+#ifndef CONTINUABLE_DETAIL_ERASURE_HPP_INCLUDED
+#define CONTINUABLE_DETAIL_ERASURE_HPP_INCLUDED
+
+#include <type_traits>
+#include <utility>
+#include <function2/function2.hpp>
+#include <continuable/detail/core/base.hpp>
+#include <continuable/detail/features.hpp>
+#include <continuable/detail/utility/traits.hpp>
+
+namespace cti {
+namespace detail {
+namespace erasure {
+template <typename... Args>
+using callback_erasure_t =
+    fu2::function_base<true, false, fu2::capacity_none, true, false,
+                       void(Args...)&&, void(exception_arg_t, exception_t) &&>;
+
+#ifdef CONTINUABLE_HAS_IMMEDIATE_TYPES
+template <typename... Args>
+using callback = callback_erasure_t<Args...>;
+#else
+template <typename... Args>
+class callback;
+
+template <typename T>
+struct is_callback : std::false_type {};
+template <typename... Args>
+struct is_callback<callback<Args...>> : std::true_type {};
+
+template <typename... Args>
+class callback : public callback_erasure_t<Args...> {
+public:
+  using erasure_t = callback_erasure_t<Args...>;
+  erasure_t erasure_;
+
+  callback() = default;
+  ~callback() = default;
+  callback(callback const&) = delete;
+  callback(callback&&) = default;
+  callback& operator=(callback const&) = delete;
+  callback& operator=(callback&&) = default;
+
+  template <
+      typename T,
+      std::enable_if_t<std::is_convertible<T, erasure_t>::value>* = nullptr,
+      std::enable_if_t<!is_callback<traits::unrefcv_t<T>>::value>* = nullptr>
+  /* implicit */ callback(T&& callable) : erasure_(std::forward<T>(callable)) {
+  }
+
+  template <
+      typename T,
+      std::enable_if_t<std::is_assignable<erasure_t, T>::value>* = nullptr,
+      std::enable_if_t<!is_callback<traits::unrefcv_t<T>>::value>* = nullptr>
+  callback& operator=(T&& callable) {
+    erasure_ = std::forward<T>(callable);
+    return *this;
+  }
+
+  void operator()(Args... args) && {
+    std::move(erasure_)(std::move(args)...);
+  }
+
+  void operator()(exception_arg_t exception_arg, exception_t exception) && {
+    std::move(erasure_)(exception_arg, std::move(exception));
+  }
+};
+#endif
+
+template <typename... Args>
+struct continuation_capacity {
+  using type = union {
+    void* pointer_;
+    base::ready_continuation<Args...> continuation_;
+  };
+
+  static constexpr std::size_t capacity = sizeof(type);
+  static constexpr std::size_t alignment = alignof(type);
+};
+
+template <typename... Args>
+using continuation_erasure_t = fu2::function_base<
+    true, false, continuation_capacity<Args...>, true, false,
+    void(promise_base<callback<Args...>, signature_arg_t<Args...>>),
+    bool(is_ready_arg_t) const, std::tuple<Args...>(query_arg_t)>;
+
+#ifdef CONTINUABLE_HAS_IMMEDIATE_TYPES
+template <typename... Args>
+using continuation = continuation_erasure_t<Args...>;
+#else
+template <typename... Args>
+class continuation;
+
+template <typename T>
+struct is_continuation : std::false_type {};
+template <typename... Args>
+struct is_continuation<continuation<Args...>> : std::true_type {};
+
+template <typename... Args>
+class continuation {
+  using erasure_t = continuation_erasure_t<Args...>;
+  erasure_t erasure_;
+
+public:
+  continuation() = default;
+  ~continuation() = default;
+  continuation(continuation const&) = delete;
+  continuation(continuation&&) = default;
+  continuation& operator=(continuation const&) = delete;
+  continuation& operator=(continuation&&) = default;
+
+  template <
+      typename T,
+      std::enable_if_t<std::is_convertible<T, erasure_t>::value>* = nullptr,
+      std::enable_if_t<!is_continuation<traits::unrefcv_t<T>>::value>* =
+          nullptr>
+  /* implicit */ continuation(T&& callable)
+      : erasure_(std::forward<T>(callable)) {
+  }
+
+  template <
+      typename T,
+      std::enable_if_t<std::is_assignable<erasure_t, T>::value>* = nullptr,
+      std::enable_if_t<!is_continuation<traits::unrefcv_t<T>>::value>* =
+          nullptr>
+  continuation& operator=(T&& callable) {
+    erasure_ = std::forward<T>(callable);
+    return *this;
+  }
+
+  void operator()(promise_base<callback<Args...>, //
+                               signature_arg_t<Args...>>
+                      promise) {
+    erasure_(std::move(promise));
+  }
+
+  bool operator()(is_ready_arg_t is_ready_arg) const {
+    return erasure_(is_ready_arg);
+  }
+
+  std::tuple<Args...> operator()(query_arg_t query_arg) {
+    return erasure_(query_arg);
+  }
+};
+#endif
+} // namespace erasure
+} // namespace detail
+} // namespace cti
+
+#endif // CONTINUABLE_DETAIL_ERASURE_HPP_INCLUDED

include/continuable/detail/other/testing.hpp

@@ -179,15 +179,15 @@ template <typename... Expected>
 struct assert_async_types_validator {
   template <typename... Actual>
   void operator()(Actual...) {
-    static_assert(std::is_same<traits::identity<Actual...>,
+    static_assert(std::is_same<identity<Actual...>,
-                               traits::identity<Expected...>>::value,
+                               identity<Expected...>>::value,
                   "The called arguments don't match with the expected ones!");
   }
 };
 
 template <typename C, typename... Args>
 void assert_async_types(C&& continuable,
-                        traits::identity<Args...> /*expected*/) {
+                        identity<Args...> /*expected*/) {
   assert_async_validation(std::forward<C>(continuable),
                           assert_async_types_validator<Args...>{});
 }

include/continuable/detail/other/transforms.hpp

@@ -77,7 +77,7 @@ template <typename Hint>
 class promise_callback;
 
 template <typename... Args>
-class promise_callback<traits::identity<Args...>>
+class promise_callback<identity<Args...>>
     : public future_trait<Args...> {
 
   typename future_trait<Args...>::promise_t promise_;
@@ -119,7 +119,7 @@ template <typename Data, typename Annotation>
 auto as_future(continuable_base<Data, Annotation>&& continuable) {
   // Create the promise which is able to supply the current arguments
   constexpr auto const hint =
-      base::annotation_of(traits::identify<decltype(continuable)>{});
+      base::annotation_of(identify<decltype(continuable)>{});
 
   promise_callback<std::decay_t<decltype(hint)>> callback;
   (void)hint;

include/continuable/detail/utility/flat-variant.hpp

@@ -62,7 +62,7 @@ template <typename T>
 using align_of_helper = std::integral_constant<std::size_t, alignof(T)>;
 
 template <typename... T>
-constexpr auto storage_of_impl(traits::identity<T...>) {
+constexpr auto storage_of_impl(identity<T...>) {
   constexpr auto size = max_element_of({(size_of_helper<T>::value)...});
   constexpr auto align = max_element_of({(align_of_helper<T>::value)...});
   return std::aligned_storage_t<size, align>{};
@@ -70,7 +70,7 @@ constexpr auto storage_of_impl(traits::identity<T...>) {
 
 /// Declares the aligned storage union for the given types
 template <typename... T>
-using storage_of_t = decltype(storage_of_impl(traits::identity<T...>{}));
+using storage_of_t = decltype(storage_of_impl(identity<T...>{}));
 
 /// The value fpr the empty slot
 using slot_t = std::uint8_t;

include/continuable/detail/utility/identity.hpp

@@ -0,0 +1,54 @@
+
+/*
+
+                        /~` _  _ _|_. _     _ |_ | _
+                        \_,(_)| | | || ||_|(_||_)|(/_
+
+                    https://github.com/Naios/continuable
+                                   v4.0.0
+
+  Copyright(c) 2015 - 2018 Denis Blank <denis.blank at outlook dot com>
+
+  Permission is hereby granted, free of charge, to any person obtaining a copy
+  of this software and associated documentation files(the "Software"), to deal
+  in the Software without restriction, including without limitation the rights
+  to use, copy, modify, merge, publish, distribute, sublicense, and / or sell
+  copies of the Software, and to permit persons to whom the Software is
+  furnished to do so, subject to the following conditions :
+
+  The above copyright notice and this permission notice shall be included in
+  all copies or substantial portions of the Software.
+
+  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.IN NO EVENT SHALL THE
+  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+  SOFTWARE.
+**/
+
+#ifndef CONTINUABLE_DETAIL_IDENTITY_HPP_INCLUDED
+#define CONTINUABLE_DETAIL_IDENTITY_HPP_INCLUDED
+
+#include <type_traits>
+#include <continuable/detail/features.hpp>
+
+namespace cti {
+namespace detail {
+/// A tagging type for wrapping other types
+template <typename... T>
+struct identity {};
+
+template <typename>
+struct is_identity : std::false_type {};
+template <typename... Args>
+struct is_identity<identity<Args...>> : std::true_type {};
+
+template <typename T>
+using identify = std::conditional_t<is_identity<std::decay_t<T>>::value, T,
+                                    identity<std::decay_t<T>>>;
+} // namespace detail
+} // namespace cti
+
+#endif // CONTINUABLE_DETAIL_IDENTITY_HPP_INCLUDED

include/continuable/detail/utility/traits.hpp

@@ -36,6 +36,7 @@
 #include <type_traits>
 #include <utility>
 #include <continuable/detail/features.hpp>
+#include <continuable/detail/utility/identity.hpp>
 
 namespace cti {
 namespace detail {
@@ -69,19 +70,6 @@ auto make_flat_tuple(T&&... args) {
   return std::tuple<T...>{std::forward<T>(args)...};
 }
 
-/// A tagging type for wrapping other types
-template <typename... T>
-struct identity {};
-
-template <typename>
-struct is_identity : std::false_type {};
-template <typename... Args>
-struct is_identity<identity<Args...>> : std::true_type {};
-
-template <typename T>
-using identify = std::conditional_t<is_identity<std::decay_t<T>>::value, T,
-                                    identity<std::decay_t<T>>>;
-
 #if defined(CONTINUABLE_HAS_CXX17_VOID_T)
 using std::void_t;
 #else

test/unit-test/CMakeLists.txt

@@ -17,9 +17,11 @@ target_link_libraries(test-continuable-base
 
 add_executable(test-continuable-single
   ${CMAKE_CURRENT_LIST_DIR}/single/test-continuable-connection-noinst
+  ${CMAKE_CURRENT_LIST_DIR}/single/test-continuable-forward-decl.cpp
   ${CMAKE_CURRENT_LIST_DIR}/single/test-continuable-flat-variant.cpp
   ${CMAKE_CURRENT_LIST_DIR}/single/test-continuable-result.cpp
   ${CMAKE_CURRENT_LIST_DIR}/single/test-continuable-promisify.cpp
+  ${CMAKE_CURRENT_LIST_DIR}/single/test-continuable-erasure.cpp
   ${CMAKE_CURRENT_LIST_DIR}/single/test-continuable-traverse.cpp
   ${CMAKE_CURRENT_LIST_DIR}/single/test-continuable-traverse-async.cpp)
 

test/unit-test/multi/test-continuable-base-errors.cpp

@@ -134,7 +134,7 @@ TYPED_TEST(single_dimension_tests, are_exceptions_partial_applyable) {
   handled = false;
   ASSERT_ASYNC_INCOMPLETION(
       this->supply_exception(supply_test_exception(),
-                             detail::traits::identity<int, int>{})
+                             detail::identity<int, int>{})
           .fail([&]() -> result<int, int> {
             EXPECT_FALSE(handled);
             handled = true;

test/unit-test/single/test-continuable-erasure.cpp

@@ -0,0 +1,89 @@
+
+/*
+  Copyright(c) 2015 - 2018 Denis Blank <denis.blank at outlook dot com>
+
+  Permission is hereby granted, free of charge, to any person obtaining a copy
+  of this software and associated documentation files(the "Software"), to deal
+  in the Software without restriction, including without limitation the rights
+  to use, copy, modify, merge, publish, distribute, sublicense, and / or sell
+  copies of the Software, and to permit persons to whom the Software is
+  furnished to do so, subject to the following conditions :
+
+  The above copyright notice and this permission notice shall be included in
+  all copies or substantial portions of the Software.
+
+  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.IN NO EVENT SHALL THE
+  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+  SOFTWARE.
+**/
+
+#include <memory>
+#include <utility>
+#include <test-continuable.hpp>
+
+using namespace cti;
+
+struct mypromise {
+  void operator()() && {
+  }
+
+  void operator()(exception_arg_t, exception_t) && {
+  }
+};
+
+struct my_continuation {
+  template <typename Callback>
+  void operator()(Callback&&) {
+  }
+
+  bool operator()(is_ready_arg_t) const noexcept {
+    return true;
+  }
+
+  std::tuple<> operator()(query_arg_t) {
+    return std::make_tuple();
+  }
+};
+
+TEST(single_erasure_test, is_assignable_from_promise) {
+  detail::erasure::callback<> p(mypromise{});
+  std::move(p)();
+}
+
+TEST(single_erasure_test, is_assignable_from_continuation) {
+  detail::erasure::continuation<> c(my_continuation{});
+  ASSERT_TRUE(c(is_ready_arg_t{}));
+  c(mypromise{});
+}
+
+TEST(single_erasure_test, is_constructible_from_work) {
+  bool flag = false;
+
+  work mywork([&] {
+    EXPECT_FALSE(flag);
+    flag = true;
+  });
+
+  ASSERT_FALSE(flag);
+  mywork();
+  ASSERT_TRUE(flag);
+}
+
+TEST(single_erasure_test, is_assignable_from_work) {
+  bool flag = false;
+
+  work mywork;
+
+  mywork = [&] {
+    EXPECT_FALSE(flag);
+    flag = true;
+  };
+
+  ASSERT_FALSE(flag);
+  mywork();
+  ASSERT_TRUE(flag);
+}

test/unit-test/single/test-continuable-forward-decl.cpp

@@ -0,0 +1,31 @@
+
+/*
+  Copyright(c) 2015 - 2018 Denis Blank <denis.blank at outlook dot com>
+
+  Permission is hereby granted, free of charge, to any person obtaining a copy
+  of this software and associated documentation files(the "Software"), to deal
+  in the Software without restriction, including without limitation the rights
+  to use, copy, modify, merge, publish, distribute, sublicense, and / or sell
+  copies of the Software, and to permit persons to whom the Software is
+  furnished to do so, subject to the following conditions :
+
+  The above copyright notice and this permission notice shall be included in
+  all copies or substantial portions of the Software.
+
+  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.IN NO EVENT SHALL THE
+  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+  SOFTWARE.
+**/
+
+#include <test-continuable.hpp>
+
+struct forward_decl_type_0;
+struct forward_decl_type_1;
+
+cti::continuable<forward_decl_type_0> fails_not_with_forward_decls_1();
+cti::continuable<forward_decl_type_0, forward_decl_type_1>
+fails_not_with_forward_decls_2();

test/unit-test/test-continuable.hpp

@@ -34,7 +34,7 @@
 #include <continuable/continuable-testing.hpp>
 #include <continuable/continuable.hpp>
 
-using cti::detail::traits::identity;
+using cti::detail::identity;
 using cti::detail::util::unused;
 
 inline auto to_hint(identity<> /*hint*/) {
@@ -113,9 +113,9 @@ struct provide_copyable {
 struct provide_unique {
   template <typename... Args, typename... Hint, typename T>
   auto make(identity<Args...>, identity<Hint...>, T&& callback) {
-    return cti::make_continuable<Hint...>(
+    return cti::make_continuable<Hint...>([
-        [callback = std::forward<T>(callback),
+      callback = std::forward<T>(callback), guard = std::make_unique<int>(0)
-         guard = std::make_unique<int>(0)](auto&&... args) mutable {
+    ](auto&&... args) mutable {
       (void)(*guard);
       return std::move(callback)(std::forward<decltype(args)>(args)...);
     });

tools/travis-ci.sh

@@ -56,7 +56,7 @@ function renew_build {
   # Configure the project and build it
   cmake -GNinja -DCMAKE_CXX_FLAGS="$STD_CXX_FLAGS $CMAKE_CXX_FLAGS -Werror" -DCMAKE_EXE_LINKER_FLAGS="$STD_LINKER_FLAGS" \
         -DCTI_CONTINUABLE_WITH_NO_EXCEPTIONS=$WITH_NO_EXCEPTIONS -DCTI_CONTINUABLE_WITH_EXPERIMENTAL_COROUTINE=$WITH_AWAIT -DCTI_CONTINUABLE_WITH_LIGHT_TESTS=$WITH_LIGHT_TESTS \
-        -DCMAKE_EXPORT_COMPILE_COMMANDS=ON -DCMAKE_BUILD_TYPE=Debug ..
+        -DCMAKE_EXPORT_COMPILE_COMMANDS=ON -DCMAKE_BUILD_TYPE=$BUILD_CONFIG ..
 }
 
 if [[ $CXX == *"clang"* ]]; then