This condition will always return 'false' since the types 'true' and 'false' have no overlap

**TypeScript Version: "typescript": "^3.2.2"

This is an asynchronous method that controls its pause externally, so it needs to be removed at the right time. However, an error warning was given to indicate that this method is not feasible.

  public async show() {
    this.showing = true;
    while (this.showing) {
      for (const frameKey in DogDto.EffectSaveInfo) {
        // [ts] This condition will always return 'false' since the types 'true' and 'false' have no overlap.
        if (this.showing === false) {
          this.container.removeAllChildren();
          break;
        }
        const frameInfo = DogDto.EffectSaveInfo[frameKey];
        const frameIndex = Number(frameKey);
        const frameBitmap = await BitmapUtils.getBitmap(DogDto.EffetcSaveImageList[frameIndex]);
        frameBitmap.x = -1 * frameInfo.origin.x;
        frameBitmap.y = -1 * frameInfo.origin.y;
        container.removeAllChildren();
        container.addChild(frameBitmap);
        await LarkDate.delay(frameInfo.delay);
      }
    }
  }
  public hide() {
    this.showing = false;
  }

usage

  public async showEffect() {
    this.effectSave.show();
    await LarkDate.delay(3 * 1000);
    this.effectSave.hide();
  }

Looks like control flow needs to be more pessimistic around await.

Temporarily changed to recursive writing :)

  public async show() {
    this.showing = true;
    const container = this.container;
    const frame = DogDto.EffetcSaveImageList[0];
    const frameInfo = DogDto.EffectSaveInfo[0];
    const bitmap = await BitmapUtils.getBitmap(frame);
    bitmap.x = -1 * frameInfo.origin.x;
    bitmap.y = -1 * frameInfo.origin.y;
    container.addChild(bitmap);
    await this.play();
  }
  public hide() {
    this.showing = false;
  }
  private async play() {
    const container = this.container;
    for (const frameKey in DogDto.EffectSaveInfo) {
      const frameInfo = DogDto.EffectSaveInfo[frameKey];
      const frameIndex = Number(frameKey);
      const frameBitmap = await BitmapUtils.getBitmap(DogDto.EffetcSaveImageList[frameIndex]);
      frameBitmap.x = -1 * frameInfo.origin.x;
      frameBitmap.y = -1 * frameInfo.origin.y;
      container.removeAllChildren();
      container.addChild(frameBitmap);
      if (this.showing === false) {
        this.container.removeAllChildren();
        break;
      }
      await LarkDate.delay(frameInfo.delay);
    }
    if (this.showing === true) {
      await this.play();
    }
  }

This is basically the same as calling a function, method or callback that could modify a narrowed variable. There should be plenty of duplicate issues, IIRC there was at least one regarding await.

The proposed solution was using a method to retrieve the value instead of accessing the property directly.

yes, it work ...

class Test{
  private status = false;
  public async test(){
    while(this.status){
      if(this.getStatus() === false){
        break;
      }
    }
  }
  private getStatus(){
    return this.status;
  }
}

Looks like control flow needs to be more pessimistic around await.

Why isn't this the correct answer? I understand the workaround, but it doesn't seem like it should be necessary. Not only does narrowing across await cause valid code to be rejected, it doesn't detect potential bugs due to narrowed values changing.

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This condition will always return 'false' since the types 'true' and 'false' have no overlap #29155

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This condition will always return 'false' since the types 'true' and 'false' have no overlap #29155

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weswigham commented on Dec 26, 2018

txiaocao commented on Dec 26, 2018

ajafff commented on Dec 26, 2018

txiaocao commented on Dec 26, 2018

trevorr commented on Jun 8, 2022

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