Resolve ready continuables directly in sequential connections

include/continuable/continuable-traverse-async.hpp

@@ -74,7 +74,7 @@ using async_traverse_in_place_tag =
 ///    ```cpp
 ///    struct my_async_visitor {
 ///      /// The synchronous overload is called for each object,
-///      /// it may return false to suspend the current control.
+///      /// it may return false to suspend the current control flow.
 ///      /// In that case the overload below is called.
 ///      template <typename T>
 ///      bool operator()(async_traverse_visit_tag, T&& element) {

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

@@ -85,7 +85,11 @@ public:
       : continuable_(std::move(continuable)) {
   }
 
-  continuable_base<Data, traits::identity<>>&& fetch() {
+  auto const& peek() const {
+    return continuable_;
+  }
+
+  auto&& fetch() {
     return std::move(continuable_);
   }
 
@@ -97,8 +101,7 @@ public:
   }
 };
 template <typename Data, typename First>
-class continuable_box<
-    continuable_base<Data, traits::identity<First>>> {
+class continuable_box<continuable_base<Data, traits::identity<First>>> {
 
   continuable_base<Data, traits::identity<First>> continuable_;
   lazy_value_t<First> first_;
@@ -109,7 +112,11 @@ public:
       : continuable_(std::move(continuable)) {
   }
 
-  continuable_base<Data, traits::identity<First>>&& fetch() {
+  auto const& peek() const {
+    return continuable_;
+  }
+
+  auto&& fetch() {
     return std::move(continuable_);
   }
 
@@ -125,20 +132,21 @@ template <typename Data, typename First, typename Second, typename... Rest>
 class continuable_box<
     continuable_base<Data, traits::identity<First, Second, Rest...>>> {
 
-  continuable_base<Data, traits::identity<First, Second, Rest...>>
-      continuable_;
+  continuable_base<Data, traits::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, traits::identity<First, Second, Rest...>>&&
           continuable)
       : continuable_(std::move(continuable)) {
   }
 
-  continuable_base<Data, traits::identity<First, Second, Rest...>>&&
-  fetch() {
+  auto const& peek() const {
+    return continuable_;
+  }
+
+  auto&& fetch() {
     return std::move(continuable_);
   }
 

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

@@ -94,9 +94,19 @@ public:
 
   template <typename Box, std::enable_if_t<aggregated::is_continuable_box<
                               std::decay_t<Box>>::value>* = nullptr>
-  bool operator()(async_traverse_visit_tag, Box&& /*box*/) {
+  bool operator()(async_traverse_visit_tag, Box&& box) {
+    if (base::attorney::is_ready(box.peek())) {
+      // The result can be resolved directly
+      traits::unpack(
+          [&](auto&&... args) mutable {
+            box.assign(std::forward<decltype(args)>(args)...);
+          },
+          base::attorney::query(box.fetch()));
+      return true;
+    } else {
       return false;
     }
+  }
 
   template <typename Box, typename N>
   void operator()(async_traverse_detach_tag, Box&& box, N&& next) {

include/continuable/detail/core/base.hpp

@@ -178,6 +178,16 @@ struct attorney {
   static Data&& consume(continuable_base<Data, Annotation>&& continuation) {
     return std::move(continuation).consume();
   }
+
+  template <typename Continuable>
+  static bool is_ready(Continuable&& continuation) noexcept {
+    return util::as_const(continuation.data_)(is_ready_arg_t{});
+  }
+
+  template <typename Data, typename Annotation>
+  static auto query(continuable_base<Data, Annotation>&& continuation) {
+    return std::move(continuation).consume()(query_arg_t{});
+  }
 };
 
 /// Returns the signature hint of the given continuable