Builder

Hello,

In the previous article, we explored the theory of the builder pattern.

Let’s see a more concrete example :

Let’s assuming that we are building a Role Playing Game core model. Here are the basic rules:

  • A player can be a Hero : a Warrior, a Wizard, or a Thief (we keep it simple)
  • Every Hero has 4 main characteristics: Health, Strength, Spirit, and Speed, that are counted in points.
  • Heroes have a Level, and starting characteristics are based on this level (Health starts at Level * 10, Strength and Spirit start at Level * 5, and Speed starts at Level * 3)
  • Warrior has a (+2 Strength, -2 Spirit) Modificator, Wizard has (+2 Spirit, -2 Strength) Modificator
  • Player can improve 2 Characteristics of 1 points each or 1 characteristic of 2 points, in order to cutomize his Hero.

A naive implementation of the Hero class would be :

Let’s focus on the Hero Creation : Every Heroes are of the same kind : Indeed, despite the different classes, every Hero has the same kind of characteristics. So, there is no need for a specific class reflecting the “Hero Class”.

Here is a first test (Note that I use Fixie test framework and Shouldly assertion library, i’ll post about it soon):

We want to be sure that our builder can build a warrior. So the implementation is straight-forward :

Obviously, we can add the methods for the other classes (keep in mind that the scope is really thin). Next step would be to ensure we cannot build a Hero without a class. The test would be :

So we update the Builder accordingly :

The guard occurs in the Create Method because it’s the most convenient place to place it, for the moment.

By following our “Business Rules”, we end-up with this kind of class :

We actually built a Domain-Specific-Language for our Hero Creation Context. This could seem a bit complex for the purpose at the first sight, but we do acheive a complete separation between the complexity of building a Hero and the behavior of the Hero later in the game.  To illustrate this, we can take a look to a potential implementation of a game client :

In this article, we saw how to implement the Builder Design Pattern in C# in a Fluent Interface way.

You can find the source code in this github repository