[core] implement ask pattern in actor

1 files changed, 12 insertions, 0 deletions

diff --git a/include/mbgl/actor/actor.hpp b/include/mbgl/actor/actor.hpp
index 810114c513..00e1bb82f8 100644
--- a/include/mbgl/actor/actor.hpp
+++ b/include/mbgl/actor/actor.hpp
@@ -6,6 +6,7 @@
 #include <mbgl/util/noncopyable.hpp>
 
 #include <memory>
+#include <future>
 
 namespace mbgl {
 
@@ -61,6 +62,17 @@ public:
         mailbox->push(actor::makeMessage(object, fn, std::forward<Args>(args)...));
     }
 
+    template <typename Fn, class... Args>
+    auto ask(Fn fn, Args&&... args) {
+        // Result type is deduced from the function's return type
+        using ResultType = typename std::result_of<decltype(fn)(Object, Args...)>::type;
+
+        std::promise<ResultType> promise;
+        auto future = promise.get_future();
+        mailbox->push(actor::makeMessage(std::move(promise), object, fn, std::forward<Args>(args)...));
+        return future;
+    }
+
     ActorRef<std::decay_t<Object>> self() {
         return ActorRef<std::decay_t<Object>>(object, mailbox);
     }