I would say that "inheritance" was much developed in Smalltalk, and there it was not really a tool for improving performance. Rather it is a conceptual tool. "

I would say that "inheritance" was much developed in Smalltalk, and there it was not really a tool for improving performance. Rather it is a conceptual tool. "Inheritance" is really the expression of Abstraction in code. Superclass is more general, and thus the abstraction of its subclasses. Although Smalltalk did not have a specific keyword for "Abstract Class" it used the convention of calling "subclassResponsibility" on methods defined in abstract subperclasses which had to be implemented in subclasses. Abstraction, generalization, these are conceptual tools. I'm not sure how "composition" models abstraction if at all. Only OOP does. And one could think that abstraction is a tool valued by scientists. No?