class Entity : public IEntity { public: int GetId() const override { return m_id; } private: int m_id; };In this code snippet, the `GetId()` method is defined as `const override` to ensure that it cannot modify the internal state of the class. It simply returns the value of the `m_id` member variable. The package library that provides `IEntity` interface and its methods like `GetId()` may vary according to the game engine framework. For example, in the Unreal Engine, `IEntity` is a part of the `UnrealEd` module, which is included in the `UnrealEngine` package library. In Unity3D game engine, `IEntity` interface may not found explicitly, but their GameObjects act like entities and can be uniquely identified by their instance IDs.