Who said that you have to use inheritance for shapes? I do know that it is an often used example, but similarly to Animal/Bird it has no real world relevance.

Who said that you have to use inheritance for shapes? I do know that it is an often used example, but similarly to Animal/Bird it has no real world relevance. I would even argue that inheritance is not the most important feature of OOP, but objects are. Inheritance is useful, for example GUI Nodes are famously good fit for it, but object encapsulation is the essential feature, missing that would pretty much disallow large swathes of programs from existing.