Design Patterns

Decorator

Each layer adds O(1) extra work (a constant amount). So n layers cost O(n) total — the total time grows along with the number of layers.

The idea, in plain English

A decorator works like wrapping a gift. You start with a plain box, then add wrapping paper, then a bow. Each layer adds something extra without changing what's inside. In code, a decorator wraps a simple object and adds extra behavior, one layer at a time.

How it works

1Start with a simple base thing that does the core job.
2Wrap it in a decorator that calls the base and adds a bit extra.
3Wrap that result in another decorator, and so on. Each layer adds one more thing.

When you'd use it

Use this when you want to add features — like logging, milk in a coffee, or extra formatting — without changing the original code. You can then mix and match those extras freely.

Common beginner mistakes

Don't stack so many decorators that no one can tell what the final behavior actually is.
Always call the wrapped thing inside your decorator, or the original behavior gets lost.

Try it — edit and run

Click the code to edit · press ⌘/Ctrl+↵ to run

Expected output — hit Run to try it

Coffee + Milk + Sugar

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