计算属性,前面已经提到过一些.大致和 oc 中的 set 和get 方法差不多,读取和赋值等

//点
 
struct Point{
    var x = 100
    var y = 100
}
var point = Point()
print(point)
 
 
// 宽高
struct Size{
    var width = 100
    var height = 100
}
var size = Size()
print(size)
 
//区域
struct Rect{
    var size = Size()
    var origin = Point()
 
    var center:Point{
 
        // 只写 get 方法,就会是只读属性
        get {
            let x = rect.origin.x + rect.size.width/2
            let y = rect.origin.y + rect.size.height/2
            return Point(x: x,y: y )
        }
        //set 只是通过一种途径来修改属性的值
        set(newValue) {
 
            let x = newValue.x - size.width/2
            let y = newValue.y - size.height/2
            origin = Point(x: x,y:y)
 
 
        }
    }
 
 
 
}
var rect = Rect()
print(rect)
 
 
 
//求区域中心点
 
 
 
var p = Point(x: 100,y: 100)
var s = Size(width: 100,height: 100)
var r = Rect(size: s,origin: p)
print(r.center)
r.center = Point(x: 10,y: 10)
print(r.origin)