Conditional Builder Design Pattern

Have you ever wanted to use the Builder design pattern to create a really cool fluent interface for building objects but you wanted to add conditions to the building? The good news is that you can do something like so:

	var level = new Random().Next(1, 20);
	var ninjaBuilder = NinjaBuilder
	.CreateNinjaBuilder()
	.AtLevel(level)
	.WithShurikens(10)
	.WithSkill("hideinshadows")
	.When(() => level > 5);
	var ninja = ninjaBuilder.Build();

view raw gistfile1.cs hosted with ❤ by GitHub

Notice how in this contrived example a ninja only gets the "hide in shadows" skill after reaching 6th level? To handle a conditional builder take a look at the following code:

	public class NinjaBuilder
	{
	private readonly List<Action<Ninja>> _builderActions;
	public static NinjaBuilder CreateNinjaBuilder()
	{
	return new NinjaBuilder();
	}
	public NinjaBuilder()
	{
	_builderActions = new List<Action<Ninja>>();
	}
	public NinjaBuilder AtLevel(int level)
	{
	_builderActions.Add(n => n.Level = level);
	return this;
	}
	public NinjaBuilder WithShurikens(int numShirukens)
	{
	_builderActions.Add(n => n.Shirukens = numShirukens);
	return this;
	}
	public NinjaBuilder WithSkill(string skill)
	{
	_builderActions.Add(s => s.Skill = skill);
	return this;
	}
	public NinjaBuilder When(Func<Boolean> condition)
	{
	var result = condition.Invoke();
	if (!result)
	{
	var oldAction = _builderActions[_builderActions.Count - 1];
	_builderActions.Remove(oldAction);
	}
	return this;
	}
	public Ninja Build()
	{
	var ninja = new Ninja();
	_builderActions.ForEach(ba => ba(ninja));
	return ninja;
	}

view raw gistfile1.cs hosted with ❤ by GitHub

For a complete sample project check it out on my GitHub account!