johnnystefan/pattern-decorator

Skill: Implement Decorator Pattern

Purpose

Attaches new behaviors to objects dynamically by placing them inside special wrapper objects that contain the behaviors.

Procedural Instructions

1. Identify Layers: Look for a primary component and optional "add-on" features.
2. Define Component Interface: Common interface for both the core object and its wrappers.
3. Create Base Decorator: A class that wraps a component and delegates all work to it.
4. Implement Concrete Decorators: Classes that override base methods to add behavior before/after delegation.

TypeScript Example

interface Notifier {
  send(msg: string): void;
}

class SimpleNotifier implements Notifier {
  send(msg: string) {
    console.log(`Sending: ${msg}`);
  }
}

class BaseDecorator implements Notifier {
  constructor(protected wrappee: Notifier) {}
  send(msg: string) {
    this.wrappee.send(msg);
  }
}

class SMSDecorator extends BaseDecorator {
  send(msg: string) {
    super.send(msg);
    console.log(`SMS: ${msg}`);
  }
}

Payoff

• Flexibility: Add/remove responsibilities at runtime.
• Composition over Inheritance: Avoids bloating classes with every possible combination of features.