struct CenterPointer{
var x = 0, y = 0
}
func + (left:CenterPointer, right:CenterPointer) -> CenterPointer{
return CenterPointer(x:left.x + right.x, y:left.y + right.y)
}
let zPointer = CenterPointer(x:2, y:3)
let yPointer = CenterPointer(x:5, y:3)
let xPointer = zPointer + yPointer
prefix func - (cPointer:CenterPointer) -> CenterPointer{
return CenterPointer(x:-cPointer.x, y:-cPointer.y)
}
let zzPointer = CenterPointer(x:2, y:3)
let yyPointer = -zPointer
func += (inout left:CenterPointer, right: CenterPointer){
left = left + right
}
var zzzPointer = CenterPointer(x:2, y:1)
zzzPointer += zzzPointer
func == (left:CenterPointer, right:CenterPointer) -> Bool{
return (left.x == right.x) && (left.y == right.y)
}
func != (left:CenterPointer, right:CenterPointer) -> Bool{
return !(left == right)
}
原文：http://www.cnblogs.com/lianfu/p/5041021.html