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import UIKit
class ViewController: UIViewController {
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view, typically from a nib.
}
override func viewWillAppear(_ animated: Bool) {
super.viewWillAppear(animated);
let str = getStr(param: true);//返回值不可以为空时,使用:String
let str2:String? = getStr2(true);//返回值可以为空时,使用:String? 使用String?类型的变量,需要加!
print(str,str2!);//hello world
//world
//1.截取开头
print(String(str2!.prefix(2)));//wo
//2.截取结尾
print(String(str2!.suffix(2)));//ld
//3.截取中间
let res = (str2! as NSString).substring(with: NSMakeRange(1, str2!.count-1));//转换为NSString 调用substring
print(res);
}
func getStr(param:Bool) -> String {//返回值没有问号,表示一定不能为空
if param {
return "hello"
}
//return nil //Nil is incompatible with return type 'String'
return ""
}
//_参数,使用时可以不用传递参数名称
func getStr2(_ param:Bool) -> String?{//加问号,表示返回值可以为空
if param{
return "world"
}
return nil
}
}