“Many people think “object-oriented programming” is synonymous with “classes”. Definitions of OOP tend to feel like credos of opposing religious denominations, but a fairly non-contentious take on it is that OOP lets you define “objects” which bundle data and code together. Compared to structured languages like C and functional languages like Scheme, the defining characteristic of OOP is that it tightly binds state and behavior together. You may think classes are the one and only way to do that, but a handful of guys including Dave Ungar and Randall Smith beg to differ. They created a language in the 80s called Self. While as OOP as can be, it has no classes.”