I don’t know if what I’m proposing in this question is a bad idea or not or even reasonable to ask because I don’t have enough experience with C++ to know any better, but I digress for the sake of getting to the point of this post.

I’m currently working on a rudimentary game engine in cooperation with the SDL2 framework for my own personal small-scale game projects. This is important to note because my question makes a clear distinction between engine classes and front-end classes. The only difference relevant to this question is that front-end classes exist on a per-project basis and are aware of all engine classes whereas engine classes are the same set of classes for every project and are therefore not aware of any specific front-end classes that may exist.

I have two engine classes: Entity and EntityFactory<typename T> (where of course T is only ever intended to be Entity or some derivative of Entity). The idea for the front-end developer is that they make a class like Man that derives from Entity, that Man class ONLY being constructable via a call to new Man() in EntityFactory<Man>. To achieve construction exclusivity as I described, I could make the default Entity constructor private and then make EntityFactory<typename T> a friend of Entity, but then Man ALSO needs to let EntityFactory<typename T> be his friend (or at least let EntityFactory<Man> be his friend). That part I don’t mind so much since the program will not compile UNTIL Man becomes a friend of EntityFactory<typename T>, the problem I have is that Man can define any constructors he wants and then other front-end classes can construct a Man without doing so through EntityFactory<Man>. None of this would be a problem if the design didn’t require new types of Entity to be derived from Entity, but I really like that about the design and I don’t want it to change.

How can I, by ONLY editing engine classes Entity and EntityFactory<typename T>, make sure classes like Man cannot define ANY new constructors that would allow Man to be constructed by anything other than a call to new Man() in EntityFactory<Man>? CAN this even be done?

If what I’m asking for IS in fact impossible, I would appreciate answers as to how to achieve the concept of ‘Factory that makes mostly the same thing but front-end classes can define slight variations of the thing that the factory makes`.

Many thanks for reading! 🙂