core: rename mbgl directories to mln (#4511)

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

include/mln/actor/optional_actor.hpp

@@ -0,0 +1,82 @@
+#pragma once
+
+#include <mln/actor/actor.hpp>
+#include <mln/actor/optional_actor_ref.hpp>
+
+namespace mln {
+
+class TaggedScheduler;
+
+template <class Object>
+class OptionalActor {
+public:
+    template <class... Args>
+    OptionalActor(bool syncObject, Scheduler& scheduler, Args&&... args) {
+        if (syncObject) {
+            object = std::make_unique<SyncObject>(std::forward<Args>(args)...);
+            selfRef = OptionalActorRef(object->self());
+        } else {
+            actor = std::make_unique<Actor<Object>>(scheduler, std::forward<Args>(args)...);
+            selfRef = OptionalActorRef(actor->self());
+        }
+    }
+
+    template <class... Args>
+    OptionalActor(bool syncObject, const TaggedScheduler& scheduler, Args&&... args) {
+        if (syncObject) {
+            object = std::make_unique<SyncObject>(std::forward<Args>(args)...);
+            selfRef = OptionalActorRef(object->self());
+        } else {
+            actor = std::make_unique<Actor<Object>>(scheduler, std::forward<Args>(args)...);
+            selfRef = OptionalActorRef(actor->self());
+        }
+    }
+
+    template <class... Args>
+    OptionalActor(bool syncObject, std::shared_ptr<Scheduler> scheduler, Args&&... args) {
+        if (syncObject) {
+            object = std::make_unique<SyncObject>(std::forward<Args>(args)...);
+            selfRef = OptionalActorRef(object->self());
+        } else {
+            actor = std::make_unique<Actor<Object>>(scheduler, std::forward<Args>(args)...);
+            selfRef = OptionalActorRef(actor->self());
+        }
+    }
+
+    OptionalActor(const OptionalActor&) = delete;
+
+    const OptionalActorRef<Object>& self() { return selfRef; }
+
+private:
+    class SyncObject {
+    public:
+        template <class... Args>
+        SyncObject(Args&&... args)
+            requires(std::is_constructible_v<Object, OptionalActorRef<Object>, Args...>)
+        {
+            new (&objectStorage) Object(OptionalActorRef(self()), std::forward<Args>(args)...);
+        }
+
+        template <class... Args>
+        SyncObject(Args&&... args)
+            requires(std::is_constructible_v<Object, Args...>)
+        {
+            new (&objectStorage) Object(std::forward<Args>(args)...);
+        }
+
+        SyncObject(const SyncObject&) = delete;
+
+        ~SyncObject() { self().~Object(); }
+
+        Object& self() { return reinterpret_cast<Object&>(objectStorage); }
+
+    private:
+        std::aligned_storage_t<sizeof(Object)> objectStorage;
+    };
+
+    std::unique_ptr<SyncObject> object;
+    std::unique_ptr<Actor<Object>> actor;
+    OptionalActorRef<Object> selfRef;
+};
+
+} // namespace mln