Chapter3

Gear.5.ts

class Gear {
  private _wheel: Wheel;

  constructor(
    readonly chainring: number,
    readonly cog: number,
    readonly rim: number,
    readonly tire: number
  ) {}

  get ratio() {
    return this.chainring / this.cog;
  }

  get gearInches() {
    return this.ratio * this.wheel.diameter;
  }

  private get wheel() {
    if (this._wheel === undefined) {
      this._wheel = new Wheel(this.rim, this.tire);
    }
    return this._wheel;
  }
}

class Wheel {
  constructor(readonly rim: number, readonly tire: number) {}

  get diameter() {
    return this.rim * (this.tire * 2);
  }
}