Investigate replacing 'SubitizeGameLevel | CountingGameLevel' with NumberPlayGameLevel

[pixelzoom]

For #84

• Is inheritance used where appropriate? Does the type hierarchy make sense?

In CountingGameLevel.js:

  public step( dt: number ): void {
  }

I wondered why this no-op step method is here. I'm guessing that it's because in NumberPlayGameModel.js, you're expecting all levels to have a step method:

  public step( dt: number ): void {
    this.levels.forEach( level => level.step( dt ) );
  }

If that's the case, then step should be part of the NumberPlayGameLevel base class API, either as a default no-op implementation, or abstract. Ditto for reset, which should be public in NumberPlayGameLevel.

Then I noticed in NumberPlayGameModel.js:

  public readonly levels: Array<SubitizeGameLevel | CountingGameLevel>;
  public readonly levelProperty: Property<SubitizeGameLevel | CountingGameLevel | null>

It seems to me that there are a lot of places where you're using SubitizeGameLevel | CountingGameLevel that could be NumberPlayGameLevel. But you're missing some things that should be in the NumberPlayGameLevel API:

• step
• reset should be public
• ??

[Luisav1]

@chrisklus and I worked on this together. We weren't able to add the step function in the base class as an abstract without overriding it as a no-op in CountingGameLevel, so we just made it no-op in the base class and deleted it from CountingGameLevel. After that and making reset() public, we were able to use NumberPlayGameLevel as the parameter type everywhere. Closing.