diposable-computed.ts

class ShortLived {
  @observable
  private isDisposed = false;

  constructor(readonly longLived) {
    this.longLived = longLived;
  }

  @computed({ keepAlive: true })
  get bar() {
    if (this.isDisposed) {
      throw new Error("Disposed");
    }
    return this.longLived.foo * 2;
  }

  dispose() {
    this.isDisposed = true;

    // Re-evaluate bar so it removes itself from all observables it
    // previously observed.
    try {
      this.bar;
    } catch (e) {}
  }
}