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The children of `EntityGroup` should extend from `EntityBase&lt;T&gt;` so I can have both `Entity`s and `EntityGroup`s in there.

ruckustboom: <https://en.wikipedia.org/wiki/Composite_pattern>

I was using something like that before, but I actually have several of these patterns that all come from the same `BaseClass` and I was hoping for more type safety. (I don't want the children of `EntityGroup` to take any `Showable`, I want to restrict it to `EntityBase`s.) Similar with `ItemGroup` and other `[Type]Group` classes.

I was suspecting that could be the case. Then use delegation instead of inheritance, put all group related stuff in a separate class and from each and every group you have, delegate to that object.

Delegation should remove a lot of boilerplate from your code.

And still you would not have to do anything weird like using `Nothing`.

`class EntityGroup : EntityBase, Group&lt;EntityBase&gt; by GroupImpl()` or something like this.