Implement continuable_base<...>::as

* Can convert continuables to other compatible signatures

include/continuable/continuable-base.hpp

@@ -404,6 +404,24 @@ public:
                                               std::forward<E>(executor));
   }
 
+  /// Returns a continuable_base which will have its signature converted
+  /// to the given Args.
+  ///
+  /// A signature can only be converted if it can be partially applied
+  /// from the previous one as shown below:
+  /// ```cpp
+  /// continuable<long> c = make_ready_continuable(0, 1, 2).as<long>();
+  /// ```
+  ///
+  /// \returns Returns a continuable_base with an asynchronous return type
+  ///          matching the given Args.
+  ///
+  /// \since 4.0.0
+  template <typename... Args>
+  auto as() && {
+    return std::move(*this).then(detail::base::convert_to<Args...>{});
+  }
+
   /// A method which allows to apply this continuable to the given callable.
   ///
   /// \param transform A transform which shall accept this continuable

include/continuable/detail/core/base.hpp

@@ -473,8 +473,10 @@ void on_executor(Executor&& executor, Invoker&& invoker, Args&&... args) {
 
   // Create a worker object which when invoked calls the callback with the
   // the returned arguments.
-  auto work = [invoker = std::forward<Invoker>(invoker),
-               args = std::make_tuple(std::forward<Args>(args)...)]() mutable {
+  auto work = [
+    invoker = std::forward<Invoker>(invoker),
+    args = std::make_tuple(std::forward<Args>(args)...)
+  ]() mutable {
     traits::unpack(
         [&](auto&&... captured_args) {
           // Just use the packed dispatch method which dispatches the work on
@@ -915,6 +917,25 @@ auto wrap_continuation(Continuation&& continuation) {
   return supplier_callback<std::decay_t<Continuation>>(
       std::forward<Continuation>(continuation));
 }
+
+/// Callback which converts its input to the given set of arguments
+template <typename... Args>
+struct convert_to {
+  std::tuple<Args...> operator()(Args... args) {
+    return std::make_tuple(std::move(args)...);
+  }
+};
+template <typename T>
+struct convert_to<T> {
+  T operator()(T arg) noexcept {
+    return std::move(arg);
+  }
+};
+template <>
+struct convert_to<> {
+  void operator()() noexcept {
+  }
+};
 } // namespace base
 } // namespace detail
 } // namespace cti

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

@@ -60,3 +60,27 @@ TYPED_TEST(single_dimension_tests, are_continuing_chainable) {
 
   ASSERT_ASYNC_TYPES(std::move(chain), tag1);
 }
+
+TYPED_TEST(single_dimension_tests, are_converted_chainable_0) {
+  auto chain =
+      this->supply().then([&] { return this->supply(tag1{}).template as<>(); });
+
+  ASSERT_ASYNC_COMPLETION(std::move(chain).then([](auto&&... args) {
+    ASSERT_EQ(sizeof...(args), 0U); //
+  }));
+}
+
+TYPED_TEST(single_dimension_tests, are_converted_chainable_1) {
+  auto chain = this->supply().then(
+      [&] { return this->supply(float(0)).template as<double>(); });
+
+  ASSERT_ASYNC_TYPES(std::move(chain), double);
+}
+
+TYPED_TEST(single_dimension_tests, are_converted_chainable_2) {
+  auto chain = this->supply().then([&] {
+    return this->supply(int(0), float(0)).template as<long, double>();
+  });
+
+  ASSERT_ASYNC_TYPES(std::move(chain), long, double);
+}