Swift Learning-基本内容

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        // 1  
        var helloMeetyou = "hello Meetyou !";
        print(helloMeetyou);
        helloMeetyou = helloMeetyou + " hahahha append";
        print(helloMeetyou);
        let cat = "";
        print(cat);

typealias myString = String;

        // 2  
        let mystring = myString(111);
        if mystring == "111" {
            print(mystring);
        }

        // 3  
        let (successCode,successDesc) = (200,"successs");
        print("successCode is \(successCode)");
        print("successDesc is \(successDesc)");

        // 4  
//        let isNil : Int? = Int("hhahah");
        let isNil : Int? = Int("404");
        if isNil != nil {
            print("isNil is a number \(isNil!)!");
        }
        //   (!) 
        if let actulyValue = isNil {
            print("actulyValue is \(actulyValue)");
        } else {
            print("isNil is empty");
        }

        // 5   &    
        // 5.1 
        let possibleString : String? = "a possible String";
        if possibleString != nil {
            print(possibleString!);
        }
        if let actuly = possibleString {
            print(actuly);
        }
        // 5.2 
        let actulyString : String! = possibleString;
        if actulyString != nil {
            print(actulyString!);
        }
        if let actylyStrubg2 = actulyString {
            print(actylyStrubg2)
        }

        // 6 do try catch
        do {
            try tryFunc();
            continueFunc();
        } catch {
            errorFunc();
        }

    // 6 do try catch
    func tryFunc() throws {
//        let optionalInt : Int? = Int("11hhh");
//        print(optionalInt!);
//        let arr = ["1","2"];
//        print(arr[4]);
        print("tryFunc");
        throw tryError.tryError1;
    }
    func continueFunc() {
        print("continueFunc");
    }
    func errorFunc() {
        print("Error :(");
    }

enum tryError : Error {
    case tryError1
}

        // 7  
        let dy = 1;
        assert(dy >= 0,"dy >= 0");
//
        // 8  
        precondition(dy >= 0,"dy > 0");

End