decorator

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Also known as

Wrapper

Attach additional responsibilities to an object dynamically. Decorators provide a flexible alternative to subclassing for extending functionality.

Use Decorator

To add responsibilities to individual objects dynamically and transparently, that is, without affecting other objects
For responsibilities that can be withdrawn
When extension by subclassing is impractical. Sometimes a large number of independent extensions are possible and would produce an explosion of subclasses to support every combination. Or a class definition may be hidden or otherwise unavailable for subclassing