Design Patterns: Decorator
The decorator pattern is a structural design pattern that can be used to add functionality to classes without modifying the original class or its interface.
From Wikipedia:
In object-oriented programming, the decorator pattern is a design pattern that allows behavior to be added to an individual object, dynamically, without affecting the behavior of other objects from the same class. The decorator pattern is often useful for adhering to the Single Responsibility Principle, as it allows functionality to be divided between classes with unique areas of concern. The decorator pattern is structurally nearly identical to the chain of responsibility pattern, the difference being that in a chain of responsibility, exactly one of the classes handles the request, while for the decorator, all classes handle the request.
“Prefer composition over inheritance” might be something you’ve heard of before, and I feel like the decorator pattern is basically the epitome of this saying. Decorators are themselves implementations of an abstraction, that also depend on the abstraction itself. This allows for “composable” pieces of behavior in that you would likely have a single “main” implementation of an abstraction, then separate “decorator” implementations that build on top of it.