class Sized: MeasureResult {}
class BaseRect: RectBlock {
    function measure(self: BaseRect, mount: Mount, constraints: Constraints): MeasureResult {
        return RectBlock.measure(self, mount, constraints)
    }
}
class WideRect: BaseRect {
    function measure(self: WideRect, mount: Object, constraints: Object): Sized {
        measured = BaseRect.measure(self, mount, constraints)
        return Sized(measured.width, measured.height)
    }
}
class Actions {
    rect: WideRect
    count: Object
    function widen(self: Actions): Unit {
        self.rect.width = 260
        self.count.increment()
    }
}
rect = WideRect(180, 60, 8, "#ED6A5A")
count = ui.state(0)
actions = Actions(rect, count)
button = Button("扩大矩形")
button.onClick(actions.widen)
root = Column(24, 16, TextBlock("参数可以更宽，返回类型可以更具体", 2), rect, button, ui.textOf(count, "value"))
page = Page()
page.title = "方法覆写契约"
page.render(root)