Correctly handle continuables with multiple results

include/continuable/detail/composition_all.hpp

@@ -206,14 +206,6 @@ constexpr auto tupelize(std::tuple<T...> arg) {
   return std::move(arg);
 }
 
-/// Lift the first tuple hierarchy inside the given tuple
-template <typename T>
-constexpr auto flatten(T&& tuple) {
-  return traits::unpack(std::forward<T>(tuple), [](auto&&... args) {
-    return std::tuple_cat(tupelize(std::forward<decltype(args)>(args))...);
-  });
-}
-
 constexpr auto deduce_from_pack(traits::identity<void>)
     -> hints::signature_hint_tag<>;
 template <typename... T>
@@ -223,15 +215,13 @@ template <typename T, std::enable_if_t<!is_tuple<T>::value>* = nullptr>
 constexpr auto deduce_from_pack(traits::identity<T>)
     -> hints::signature_hint_tag<T>;
 
-template <typename Composition>
-constexpr auto deduce_hint(Composition&& /*composition*/) {
-  using deduced_t =
-      decltype(map_pack(all_hint_deducer{}, std::declval<Composition>()));
-
-  // We must guard deduced_t against to be void since this represents an
+// We must guard the mapped type against to be void since this represents an
 // empty signature hint.
-  return decltype(deduce_from_pack(traits::identity<deduced_t>{})){};
-}
+template <typename Composition>
+constexpr auto deduce_hint(Composition && /*composition*/)
+    -> decltype(deduce_from_pack(
+        traits::identity<decltype(map_pack(all_hint_deducer{},
+                                           std::declval<Composition>()))>{})){};
 } // namespace all
 
 /// Finalizes the all logic of a given composition

include/continuable/detail/composition_remapping.hpp

@@ -56,12 +56,29 @@ namespace composition {
 namespace remapping {
 // Guard object for representing void results
 struct void_result_guard {};
+// Guard object for representing multiple results
+template <typename... Args>
+struct multi_result_guard {
+  std::tuple<Args...> result_;
+
+  multi_result_guard& operator=(std::tuple<Args...> result) {
+    result_ = std::move(result);
+    return *this;
+  }
+};
 
 // Callable object that maps void_result_guard zo zero arguments
-struct clean_void_results {
+struct unpack_result_guards {
   auto operator()(void_result_guard) const noexcept {
     return spread_this();
   }
+  template <typename... Args>
+  auto operator()(multi_result_guard<Args...> guard) const noexcept {
+    // Spread the result of the continuable into the current depth.
+    return traits::unpack(std::move(guard.result_), [](auto&&... args) {
+      return spread_this(std::forward<decltype(args)>(args)...);
+    });
+  }
 };
 
 namespace detail {
@@ -82,7 +99,8 @@ struct result_extractor_mapper {
   static constexpr auto
   initialize(hints::signature_hint_tag<First, Second, Args...>) {
     // TODO Fix non default constructible values
-    return std::make_tuple(First{}, Second{}, Args{}...);
+    return multi_result_guard<First, Second, Args...>{
+        std::make_tuple(First{}, Second{}, Args{}...)};
   }
 
   /// Remap a continuable to its corresponding result values

include/continuable/detail/composition_seq.hpp

@@ -184,8 +184,8 @@ public:
   template <typename T>
   void operator()(async_traverse_complete_tag, T&& /*pack*/) {
     // Remove void result guard tags
-    auto cleaned = all::flatten(
-        map_pack(remapping::clean_void_results{}, std::move(data_.result)));
+    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));