The problem with the "inheritance isn't part of OO" take is that every single one of the languages we call object-oriented that gained mass adoption have inheri

The problem with the "inheritance isn't part of OO" take is that every single one of the languages we call object-oriented that gained mass adoption have inheritance, including Alan Kay's own smalltalk. There have been entire books written about object-oriented design describing ways to use (or not use) inheritance in program design. So whether or not it was intended to be important by the author of the term is immaterial, it for all intents and purposes is a crucial part of object oriented languages. Inheritance is not the only problem w/ OO either, many things are straight up awkward to express when you must couple data and code together. Many 2+-argument function w/ disparate parameter types create confusion about which class "owns" the definition of the function. You also don't need to marry data and code to get the benefits of encapsulation. Many functional languages in the ML family have developed clever solutions to encapsulate the definition of a datatype while exposing it to module-local functions. There's no need for the datatype to carry a method around with it to support this.