Mixin

Reusable behavior composed into a host class in object-oriented programming, often through a trait. Scala allows one superclass and several mixed-in traits. Required abstract members let a mixin depend on host capabilities without fixing one concrete superclass; member conflicts and super calls are resolved using the language's linearization rules.

A Scala trait can intercept a method, call the next implementation through super, and add behavior before or after it. abstract override marks such an implementation as requiring an appropriate concrete method later in the class linearization. A character-counting plugin can update its cached counts only after a successful underlying document edit, preserving its additional representation invariant without changing the edit's abstract result.