Started to implement combined path callables

include/continuable/continuable-promise-base.hpp

@@ -65,6 +65,11 @@ public:
   void operator()(Args... args) {
     data_(std::move(args)...);
   }
+  /// Resolves the continuation with the given exception
+  void operator()(detail::types::dispatch_error_tag tag,
+                  detail::types::error_type exception) {
+    data_(tag, std::move(exception));
+  }
 
   /// Resolves the continuation with the given values
   void set_value(Args... args) {

include/continuable/detail/base.hpp

@@ -259,6 +259,39 @@ void packed_dispatch(Executor&& executor, Invoker&& invoker, Args&&... args) {
 }
 
 namespace callbacks {
+template <typename Base>
+struct error_handler_base {
+  void operator()(types::dispatch_error_tag, types::error_type error) {
+    // Just invoke the error handler, cancel the calling hierarchy after
+    auto invoker = [](typename Base::CallbackT&& callback,
+                      types::error_type&& error) {
+      std::move(callback)(std::move(error));
+    };
+
+    // Invoke the error handler
+    packed_dispatch(
+        std::move(static_cast<Base*>(this)->executor_), std::move(invoker),
+        std::move(static_cast<Base*>(this)->callback_), std::move(error));
+  }
+};
+
+template <typename Base, typename = void>
+struct result_callback_error_base {
+  /// The operator which is called when an error occurred
+  void operator()(types::dispatch_error_tag tag, types::error_type error) {
+    // Forward the error to the next callback
+    std::move(static_cast<Base*>(this)->next_callback_)(tag, std::move(error));
+  }
+};
+template <typename Base>
+struct result_callback_error_base<
+    Base, std::enable_if_t<util::is_invokable<
+              typename Base::Callback,
+              std::tuple<types::dispatch_error_tag, types::error_type>>::value>>
+    : error_handler_base<Base> {
+  using error_handler_base<Base>::operator();
+};
+
 template <typename Hint, typename Callback, typename Executor,
           typename NextCallback>
 struct result_callback;
@@ -266,11 +299,23 @@ struct result_callback;
 template <typename... Args, typename Callback, typename Executor,
           typename NextCallback>
 struct result_callback<hints::signature_hint_tag<Args...>, Callback, Executor,
-                       NextCallback> {
+                       NextCallback>
+    : result_callback_error_base<
+          result_callback<hints::signature_hint_tag<Args...>, Callback,
+                          Executor, NextCallback>> {
+
+  using CallbackT = Callback;
+
   Callback callback_;
   Executor executor_;
   NextCallback next_callback_;
 
+  explicit result_callback(Callback callback, Executor executor,
+                           NextCallback next_callback)
+      : callback_(std::move(callback)), executor_(std::move(executor)),
+        next_callback_(std::move(next_callback)) {
+  }
+
   /// 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
@@ -287,11 +332,7 @@ struct result_callback<hints::signature_hint_tag<Args...>, Callback, Executor,
                     std::move(args)...);
   }
 
-  /// The operator which is called when an error occurred
+  using result_callback_error_base<result_callback>::operator();
-  void operator()(types::dispatch_error_tag tag, types::error_type error) {
-    // Forward the error to the next callback
-    std::move(next_callback_)(tag, std::move(error));
-  }
 
   /// Resolves the continuation with the given values
   void set_value(Args... args) {
@@ -311,29 +352,29 @@ struct error_callback;
 template <typename... Args, typename Callback, typename Executor,
           typename NextCallback>
 struct error_callback<hints::signature_hint_tag<Args...>, Callback, Executor,
-                      NextCallback> {
+                      NextCallback>
+    : error_handler_base<error_callback<hints::signature_hint_tag<Args...>,
+                                        Callback, Executor, NextCallback>> {
+
+  using CallbackT = Callback;
+
   Callback callback_;
   Executor executor_;
   NextCallback next_callback_;
 
+  explicit error_callback(Callback callback, Executor executor,
+                          NextCallback next_callback)
+      : callback_(std::move(callback)), executor_(std::move(executor)),
+        next_callback_(std::move(next_callback)) {
+  }
+
   /// The operator which is called when the result was provided
   void operator()(Args... args) {
     // Forward the arguments to the next callback
     std::move(next_callback_)(std::move(args)...);
   }
 
-  /// The operator which is called when an error occurred
+  using error_handler_base<error_callback>::operator();
-  void operator()(types::dispatch_error_tag /*tag*/, types::error_type error) {
-
-    // Just invoke the error handler, cancel the calling hierarchy after
-    auto invoker = [](Callback&& callback, types::error_type&& error) {
-      std::move(callback)(std::move(error));
-    };
-
-    // Invoke the error handler
-    packed_dispatch(std::move(executor_), std::move(invoker),
-                    std::move(callback_), std::move(error));
-  }
 
   /// Resolves the continuation with the given values
   void set_value(Args... args) {

include/continuable/detail/transforms.hpp

@@ -34,7 +34,9 @@
 #include <future>
 
 #include <continuable/detail/api.hpp>
+#include <continuable/detail/features.hpp>
 #include <continuable/detail/hints.hpp>
+#include <continuable/detail/types.hpp>
 
 namespace cti {
 namespace detail {
@@ -90,6 +92,14 @@ public:
   void operator()(Args... args) {
     this->resolve(promise_, std::move(args)...);
   }
+#if !defined(CONTINUABLE_WITH_CUSTOM_ERROR_TYPE) &&                            \
+    !defined(CONTINUABLE_WITH_NO_EXCEPTIONS)
+  /// Resolves the promise through the exception
+  void operator()(types::dispatch_error_tag, types::error_type error) {
+    promise_.set_exception(error);
+  }
+#endif
+
   /// Returns the future from the promise
   auto get_future() {
     return promise_.get_future();

include/continuable/detail/util.hpp

@@ -73,10 +73,10 @@ struct is_invokable_impl<
 /// arguments inside lambda closures.
 ///
 /// ```cpp
-/// traits::is_invokable_t<object, std::tuple<Args...>>
+/// traits::is_invokable<object, std::tuple<Args...>>
 /// ```
 template <typename T, typename Args>
-using is_invokable_t = typename detail::is_invokable_impl<T, Args>::type;
+using is_invokable = typename detail::is_invokable_impl<T, Args>::type;
 
 namespace detail {
 /// Forwards every element in the tuple except the last one
@@ -124,7 +124,7 @@ auto partial_invoke_impl(std::false_type, T&& callable,
   auto next = forward_except_last(std::move(args));
 
   // Test whether we are able to call the function with the given tuple
-  is_invokable_t<decltype(callable), decltype(next)> is_invokable;
+  is_invokable<decltype(callable), decltype(next)> is_invokable;
 
   return partial_invoke_impl(is_invokable, std::forward<T>(callable),
                              std::move(next));
@@ -157,7 +157,7 @@ auto partial_invoke_impl_shortcut(std::false_type failed, T&& callable,
 template <typename T, typename... Args>
 auto partial_invoke(T&& callable, Args&&... args) {
   // Test whether we are able to call the function with the given arguments.
-  is_invokable_t<decltype(callable), std::tuple<Args...>> is_invokable;
+  is_invokable<decltype(callable), std::tuple<Args...>> is_invokable;
 
   // The implementation is done in a shortcut way so there are less
   // type instantiations needed to call the callable with its full signature.

test/playground/test-playground.cpp

@@ -57,7 +57,18 @@ static cti::continuable<std::string> http_request3(std::string url) {
   };
 }
 
+struct my_callable {
+  void operator()(std::string) {
+    // ...
+  }
+  void operator()(cti::dispatch_error_tag, cti::error_type) {
+    // ...
+  }
+};
+
 int main(int, char**) {
+  http_request("github.com").then(my_callable{});
+
   http_request("github.com")
       .then([](std::string) {
         // ...