Fix "all" compositions with error handling

include/continuable/detail/composition.hpp

@@ -41,6 +41,7 @@
 #include <continuable/detail/api.hpp>
 #include <continuable/detail/base.hpp>
 #include <continuable/detail/traits.hpp>
+#include <continuable/detail/types.hpp>
 
 namespace cti {
 namespace detail {
@@ -111,6 +112,7 @@ constexpr void assign(traits::size_constant<Pos> /*pos*/, T& /*storage*/) {
 template <std::size_t Pos, typename T, typename Current, typename... Args>
 void assign(traits::size_constant<Pos> pos, T& storage, Current&& current,
             Args&&... args) {
+  // TODO Improve this -> linear instantiation
   std::get<Pos>(storage) = std::forward<Current>(current);
   assign(pos + traits::size_constant_of<1>(), storage,
          std::forward<Args>(args)...);
@@ -125,6 +127,7 @@ class all_result_submitter : public std::enable_shared_from_this<
 
   T callback_;
   std::atomic<std::size_t> left_;
+  std::once_flag flag_;
   std::tuple<Args...> result_;
 
 public:
@@ -134,30 +137,50 @@ public:
 
   /// Creates a submitter which submits it's result into the tuple
   template <std::size_t From, std::size_t To>
-  auto create_callback(traits::size_constant<From> from,
+  auto create_callback(traits::size_constant<From> /*from*/,
                        traits::size_constant<To> /*to*/) {
 
-    return [ me = this->shared_from_this(), from ](auto&&... args) {
-      static_assert(sizeof...(args) == (To - From),
-                    "Submission called with the wrong amount of arguments!");
-
-      // Assign the values from the result to it's correct positions of the
-      // tuple. Maybe think about the thread safety again...:
-      // http://stackoverflow.com/questions/40845699
-      assign(from, me->result_, std::forward<decltype(args)>(args)...);
-
-      // Complete the current result
-      me->complete_one();
+    return [me = this->shared_from_this()](auto&&... args) {
+      // Resolve the and composition with the given arguments at the
+      // stored position
+      me->resolve(traits::size_constant<From>{}, traits::size_constant<To>{},
+                  std::forward<decltype(args)>(args)...);
     };
   }
 
 private:
+  template <std::size_t From, std::size_t To, typename... PartialArgs>
+  void resolve(traits::size_constant<From> from, traits::size_constant<To>,
+               PartialArgs&&... args) {
+
+    static_assert(sizeof...(args) == (To - From),
+                  "Submission called with the wrong amount of arguments!");
+
+    // Assign the values from the result to it's correct positions of the
+    // tuple. Maybe think about the thread safety again...:
+    // http://stackoverflow.com/questions/40845699
+    assign(from, result_, std::forward<PartialArgs>(args)...);
+
+    // Complete the current result
+    complete_one();
+  }
+
+  template <std::size_t From, std::size_t To>
+  void resolve(traits::size_constant<From>, traits::size_constant<To>,
+               types::dispatch_error_tag tag, types::error_type error) {
+
+    // We never complete the composition, but we forward the first error
+    // which was raised.
+    std::call_once(flag_, std::move(callback_), tag, std::move(error));
+  }
+
   // Invokes the callback with the cached result
   void invoke() {
     assert((left_ == 0U) && "Expected that the submitter is finished!");
     std::atomic_thread_fence(std::memory_order_acquire);
     traits::unpack(std::move(result_), [&](auto&&... args) {
-      std::move(callback_)(std::forward<decltype(args)>(args)...);
+      std::call_once(flag_, std::move(callback_),
+                     std::forward<decltype(args)>(args)...);
     });
   }
   // Completes one result

test/playground/test-playground.cpp

@@ -69,7 +69,7 @@ int main(int, char**) {
       .fail([](std::error_condition) {
         // ...
       })
-      .then([](int) {
+      .then([] {
         // ...
       });
 
@@ -78,10 +78,26 @@ int main(int, char**) {
         // ...
         return 0;
       })
-      .fail([](std::error_condition) {
+      .then([](int) {
         // ...
       })
-      .then([](int) {
+      .fail([](std::error_condition) {
+        // ...
+      });
+
+  (http_request("github.com") && http_request("github.com"))
+      .then([](std::string, std::string) {
+        // ...
+      })
+      .fail([](std::error_condition) {
+        // ...
+      });
+
+  (http_request("github.com") || http_request("github.com"))
+      .then([](std::string) {
+        // ...
+      })
+      .fail([](std::error_condition) {
         // ...
       });