2020-05-12

class Rectangle {

  num left, top, width, height;

  Rectangle(this.left, this.top, this.width, this.height);

  // 定义两个计算属性： right 和 bottom。

  num get right => left + width;

  set right(num value)=>left = value - width;

  num get bottom => top + height;

  set bottom(num value) => top = value - height;

}

void main() {

  var rect = Rectangle(3, 4, 20, 15);

  assert(rect.left == 3);

  rect.right = 12;

  assert(rect.left == -8);

}