anchor.diff:      value: value,
       activeColor: activeColor,
       inactiveColor: inactiveColor,
  +    activeThumbDecoration: activeThumbDecoration,
  +    inactiveThumbDecoration: inactiveThumbDecoration,
       activeTrackColor: activeTrackColor,
       inactiveTrackColor: inactiveTrackColor,
       onChanged: onChanged
  
positive.code:       ..value = value
        ..activeColor = activeColor
        ..inactiveColor = inactiveColor
        ..activeTrackColor = activeTrackColor
        ..inactiveTrackColor = inactiveTrackColor
        ..onChanged = onChanged;
  
negative.code:     bool value,
      Color activeColor,
      Color inactiveColor,
      Decoration activeThumbDecoration,
      Decoration inactiveThumbDecoration,
      Color activeTrackColor,
      Color inactiveTrackColor,
      ValueChanged<bool> onChanged
    }) : _activeThumbDecoration = activeThumbDecoration,
         _inactiveThumbDecoration = inactiveThumbDecoration,
         _activeTrackColor = activeTrackColor,
         _inactiveTrackColor = inactiveTrackColor,
         super(
           value: value,
           activeColor: activeColor,
           inactiveColor: inactiveColor,
           onChanged: onChanged,
           minRadialReactionRadius: _kThumbRadius,
           size: const Size(_kSwitchWidth, _kSwitchHeight)
         ) {
      _drag = new HorizontalDragGestureRecognizer()
        ..onStart = _handleDragStart
        ..onUpdate = _handleDragUpdate
        ..onEnd = _handleDragEnd;
    }
  
    Decoration get activeThumbDecoration => _activeThumbDecoration;
    Decoration _activeThumbDecoration;
    void set activeThumbDecoration(Decoration value) {
      if (value == _activeThumbDecoration)
        return;
      _activeThumbDecoration = value;
      markNeedsPaint();
    }
  
    Decoration get inactiveThumbDecoration => _inactiveThumbDecoration;
    Decoration _inactiveThumbDecoration;
    void set inactiveThumbDecoration(Decoration value) {
      if (value == _inactiveThumbDecoration)
        return;
      _inactiveThumbDecoration = value;
      markNeedsPaint();
    }
  
    Color get activeTrackColor => _activeTrackColor;
  