anchor.diff:    return bufferFrameCount;
   }
   
  +/// Fail COM calls that don't complete successfully.
   void check(int hr) {
     if (FAILED(hr)) throw WindowsException(hr);
   }
  
positive.code: 
    // Retrieve the default audio output device.
    final pDeviceEnumerator = MMDeviceEnumerator.createInstance();
    final ppEndpoint = calloc<Pointer<COMObject>>();
    check(pDeviceEnumerator.GetDefaultAudioEndpoint(
        0, // dataflow: rendering device
        0, // role: system notification sound
        ppEndpoint));
    pDeviceEnumerator.Release();
    free(pDeviceEnumerator.ptr);
  
    // Activate an IAudioClient interface for the output device.
    final pDevice = IMMDevice(ppEndpoint.cast());
    final iidAudioClient = convertToIID(IID_IAudioClient);
    final ppAudioClient = calloc<Pointer<COMObject>>();
    check(pDevice.Activate(iidAudioClient, CLSCTX_ALL, nullptr, ppAudioClient));
  
negative.code:   return true;
  }
  
  /// Retrieve the number of frames that the audio buffer can hold.
  int getBufferFrameCount(IAudioClient pAudioClient) {
    final pBufferFrameCount = calloc<UINT32>();
    check(pAudioClient.GetBufferSize(pBufferFrameCount));
  