Composite

Composite Pattern

Intent

Compose objects into tree structures to represent part-whole hierarchies. Composite lets clients treat individual objects and compositions uniformly.

Problem

You need to work with tree structures of objects where individual objects and groups of objects should be treated uniformly.

Solution

The Composite pattern composes objects into tree structures and allows treating individual objects and compositions of objects uniformly through a common interface.

When to Use

• You want to represent part-whole hierarchies of objects
• You want clients to ignore the difference between compositions and individual objects
• You need to implement a tree-like object structure

C# Implementation

See the Program.cs file for a graphics tree demonstrating uniform treatment of leaf and composite nodes.

Pros

• Can work with complex tree structures more conveniently
• Open/Closed Principle - introduce new element types without breaking existing code
• Clients can treat all objects uniformly

Cons

• Might be difficult to provide a common interface for classes with very different functionality
• Can make design overly general