Design Patterns: Composite

The Composite Design Pattern consists of the allowing software that executes an operation in a collection of primitive and composite objects. The easiest example to think of is a file system, you can have a directory and it may have more directories and also files in them.

One example of a composite pattern structure would be:


Figure 1: Composite Pattern Structure

The following code prints elements on the screen in a hierarchical format without having to worry about the type of the object (for example, you could print a directory and file names without being concerned with whether the object is a directory or a file).

public interface Component
{
void DoStuff(int indent);
}
public class Item : Component
{
public string Name { get; set; }
public void DoStuff(int indent)
{
Console.Write(new String(' ', indent));
Console.WriteLine(Name);
}
}
public class Composite : Component
{
public Composite()
{
Components = new List
<Component>();
}
public IList
    <Component> Components { get; set; }
public void DoStuff(int indent)
{
Console.Write(new String(' ', indent));
Console.WriteLine("
        <Group>");
foreach (var component in Components)
{
component.DoStuff(indent + 2);
}
}
}

Results:

<Group>
First
Second
<Group>
Third
<Group>
Fourth

In games it could be used to generate a skill tree or used to calculate some sort of composite attack. I found one example of it being used in the attributes system of a RPG game.