Factory Pattern to build many derived classes

Question

I have a factory object ChallengeManager to generate instances of a Challenge object for a game I\'m building. There are many challenges. The constru

Answer 1

I really like the pattern you are describing and use it often. The way I like to do it is:

abstract class Challenge 
{
  private Challenge() {} 
  private class ChallengeA : Challenge 
  {
    public ChallengeA() { ... }
  }
  private class ChallengeB : Challenge 
  {
    public ChallengeB() { ... }
  }
  public static Challenge MakeA() 
  {
    return new ChallengeA();
  }
  public static Challenge MakeB() 
  {
    return new ChallengeB();
  }
}

This pattern has many nice properties. No one can make a new Challenge because it is abstract. No one can make a derived class because Challenge's default ctor is private. No one can get at ChallengeA or ChallengeB because they are private. You define the interface to Challenge and that is the only interface that the client needs to understand.

When the client wants an A, they ask Challenge for one, and they get it. They don't need to worry about the fact that behind the scenes, A is implemented by ChallengeA. They just get a Challenge that they can use.