README.md

Decorator Pattern

Intent

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

Problem

You need to add behavior to individual objects without affecting other objects of the same class. Using inheritance to extend behavior results in a rigid, static solution.

Solution

The Decorator pattern wraps an object with another object that adds new behavior, while keeping the interface the same. Multiple decorators can be stacked to combine behaviors.

Structure

Component (interface)
└── Operation()

ConcreteComponent
└── Operation()

Decorator (implements Component)
├── component (reference to Component)
└── Operation() (calls component.Operation())

ConcreteDecorator
└── Operation() (adds behavior before/after calling base.Operation())

When to Use

• To add responsibilities to individual objects dynamically and transparently
• For responsibilities that can be withdrawn
• When extension by subclassing is impractical (class explosion)
• To add behavior without modifying existing code

C# Implementation

See the Program.cs file for an implementation example.

Pros

• More flexible than static inheritance
• Avoids feature-laden classes high up in the hierarchy
• Can add/remove responsibilities at runtime
• Single Responsibility Principle - dividing functionality between classes

Cons

• Hard to remove a specific wrapper from the wrappers stack
• Hard to implement decorator that doesn't depend on order in the stack
• Initial configuration code might look ugly with many layers