feat: add ObjectRef for scene loading to not rely on runtime id's

destrum/include/destrum/ObjectModel/GameObject.h

@@ -44,9 +44,6 @@ public:
 
     [[nodiscard]] ObjectId GetId() const { return m_Id; }
 
-    // Use this only while loading a scene.
-    void SetIdForDeserialization(ObjectId id);
-
     [[nodiscard]] Scene* GetScene() const { return m_Scene; }
 
     [[nodiscard]] std::vector<std::unique_ptr<Component>>& GetComponents() {

destrum/include/destrum/ObjectModel/ObjectRef.h

@@ -0,0 +1,37 @@
+#ifndef DESTRUM_OBJECTREF_H
+#define DESTRUM_OBJECTREF_H
+
+#include <unordered_map>
+
+#include <nlohmann/json_fwd.hpp>
+
+#include <destrum/ObjectModel/ObjectId.h>
+
+class GameObject;
+class Scene;
+
+class ObjectRef final {
+public:
+    using ObjectMap = std::unordered_map<ObjectId, GameObject*>;
+
+    ObjectRef() = default;
+    explicit ObjectRef(ObjectId id) : m_Id(id) {}
+    explicit ObjectRef(const GameObject& object);
+
+    [[nodiscard]] ObjectId GetId() const { return m_Id; }
+    [[nodiscard]] bool IsSet() const { return m_Id != InvalidObjectId; }
+
+    [[nodiscard]] GameObject* Get(const Scene& scene) const;
+
+    bool Resolve(const ObjectMap& objects);
+
+    bool operator==(const ObjectRef&) const = default;
+
+private:
+    ObjectId m_Id{InvalidObjectId};
+};
+
+void to_json(nlohmann::json& json, const ObjectRef& ref);
+void from_json(const nlohmann::json& json, ObjectRef& ref);
+
+#endif //DESTRUM_OBJECTREF_H