Decorator

The Decorator is a structural pattern. The pattern is a flexible alternative to subclassing in order to extend a class with additional functionalities.

Warning

The Decorator pattern has nothing to do with Python Decorators.

Example

You can find an example of the Decorator Pattern in the Python wiki. It shows us how decorators are built into the pipeline to dynamically insert many behaviours into an object.

Pros and cons

Pros

• Several decorators can be connected in series.

• The decorators can be exchanged at runtime and even after instantiation.

• The class to be decorated is not necessarily fixed, but its interface is.

• In addition, long and confusing inheritance hierarchies can be avoided.

Cons

• As a decorated component is not identical to the component itself, care must be taken when testing for object identity.

• When using decorated components, the messages must be forwarded from the decorator to the decorated object.