Fix an issue when connecting void continuables

include/continuable/continuable-base.hpp

@@ -800,15 +800,15 @@ constexpr auto make_ready_continuable(FirstResult&& first_result,
 /// Returns a continuable with the parameterized result which instantly
 /// resolves the promise with the given error type.
 ///
-/// \tparam FirstArg The first result of the fake signature of the
-///                  returned continuable.
-/// \tparam Rest     The rest of the result of the fake signature of the
-///                  returned continuable.
+/// \tparam Signature The fake signature of the returned continuable.
 ///
-/// \since           3.0.0
-template <typename Exception, typename FirstArg = void, typename... Rest>
+/// \since            3.0.0
+template <typename... Signature, typename Exception>
 constexpr auto make_exceptional_continuable(Exception&& exception) {
-  return make_continuable<FirstArg, Rest...>( // ...
+  static_assert(sizeof...(Signature) > 0,
+                "Requires at least one type for the fake signature!");
+
+  return make_continuable<Signature...>( // ...
       [exception = std::forward<Exception>(exception)](auto&& promise) mutable {
         std::forward<decltype(promise)>(promise).set_exception(
             std::move(exception));

include/continuable/continuable-compositions.hpp

@@ -77,10 +77,10 @@ auto when_all(Continuables&&... continuables) {
 ///     std::vector<cti::continuable<int>>{cti::make_ready_continuable(3),
 ///                                        cti::make_ready_continuable(4)},
 ///     std::make_tuple(std::make_tuple(cti::make_ready_continuable(5))))
-///     .then([](int r0, int r1, int r2, std::vector<int> r34,
-///              std::tuple<std::tuple<int>> r5) {
-///       // ...
-///     });
+///       .then([](int r0, int r1, int r2, std::vector<int> r34,
+///                std::tuple<std::tuple<int>> r5) {
+///         // ...
+///       });
 /// ```
 ///
 /// \see        continuable_base::operator>> for details.

include/continuable/detail/composition-seq.hpp

@@ -182,18 +182,33 @@ public:
           // Continue the asynchronous sequential traversal
           next();
         })
+        .fail([me = this->shared_from_this()](types::error_type exception) {
+          // Abort the traversal when an error occurred
+          std::move(me->data_.callback)(types::dispatch_error_tag{},
+                                        std::move(exception));
+        })
         .done();
   }
 
+  void finalize(traits::identity<void>) {
+    std::move(data_.callback)();
+  }
   template <typename T>
-  void operator()(async_traverse_complete_tag, T&& /*pack*/) {
-    // Remove void result guard tags
+  void finalize(traits::identity<T>) {
     auto cleaned =
         map_pack(remapping::unpack_result_guards{}, std::move(data_.result));
 
     // Call the final callback with the cleaned result
     traits::unpack(std::move(cleaned), std::move(data_.callback));
   }
+
+  template <typename T>
+  void operator()(async_traverse_complete_tag, T&& /*pack*/) {
+    // Guard the final result against void
+    using result_t = decltype(
+        map_pack(remapping::unpack_result_guards{}, std::move(data_.result)));
+    finalize(traits::identity<result_t>{});
+  }
 };
 } // namespace seq
 

test/playground/test-playground.cpp

@@ -143,11 +143,30 @@ int main(int, char**) {
     util::unused(o2);
   });
 
-  cti::when_seq()
+  cti::when_seq(cti::make_ready_continuable()) // ...
       .then([] {
         // ...
-      })
+      });
+
+  cti::when_seq() // ...
+      .then([] {
+        // ...
+      });
+
+  cti::when_seq(cti::make_exceptional_continuable<void>(std::error_condition{}))
       .fail([](auto) {
         // ...
       });
+
+  /*composition::apply_composition(
+      composition::composition_strategy_all_tag{},
+      cti::make_ready_continuable(0, 1), 2, //< See this plain value
+      std::vector<cti::continuable<int>>{cti::make_ready_continuable(3),
+                                         cti::make_ready_continuable(4)},
+      std::make_tuple(std::make_tuple(cti::make_ready_continuable(5))))
+      .then([](int r0, int r1, int r2, std::vector<int> r34,
+               std::tuple<std::tuple<int>> r5) {
+        // ...
+        util::unused(r0, r1, r2, r34, r5);
+      });*/
 }