没有怎么接触过Swift，直接上手看的代码，遇到_符号，特此记录。

let _ = 100	
var _ = 200	

for _ in 0...3 {
    print("do something...")
}

func fun1( _ x: Int, _ y: Int){
	print("do something...")
}

func add(x:Int,y:Int) -> Int{
	return x+y
}
_ = add(x: 1, y: 2)

Swift里的_(下划线)是省略符号，代表省略的意思，详细作用可看下方注释：

let _ = 100	//无实际含义
var _ = 200	//无实际含义

//循环三次，省略计数器
for _ in 0...3 {
    print("do something...")
}

//去掉参数标签
func fun1( _ x: Int, _ y: Int){
	print("do something...")
}
fun1(10,20)

//省略返回值
func add(x:Int,y:Int) -> Int{
	return x+y
}
_ = add(x: 1, y: 2)