1，通过重载加号运算符，使自定义的两个坐标结构体对象实现相加：
struct CenterPointer{
var x=0,y=0
}
func + (left:CenterPointer,right:CenterPointer) -> CenterPointer{
return CenterPointer(x:left.x+right.y,y:left.y+right.y)
}
let pointer1 = CenterPointer(x:2,y:3)
let pointer2 = CenterPointer(x:4,y:5)
let pointer3 = pointer1 + pointer2
2，重载判断运算符 ，实现判断自定义类型是否相等
func == (left:CenterPointer,right:CenterPointer) -> Bool {
return (left.x == right.x) && (left.y == right.y)
}
func != (left:CenterPointer,right:CenterPointer) -> Bool {
return !(left == right)
}
3，组合运算符 ，即将其他运算符和赋值运算符组合在一起，注意要把运算符左参数设置成inout类型
func += (inout left:CenterPointer,right:CenterPointer){
left = left + right
}
var pointer1 = CenterPointer(x:2,y:3)
var pointer2 = CenterPointer(x:4,y:5)
pointer1 += pointer2