Swift 4.0学习记录 ---> The Basics

import UIKit

class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.
        
        /// Swift 4.0学习记录 ---> The Basics
        print(self.test1(str: "测试函数1_返回字符串"))
        self.testNoParams()
        self.specialString()
        self.testTypealias()
        self.testBool(isTrue: true)
        self.testTuples()
        self.testOptional()
        
        do {
            try throwAnError()
            // no error was thrown
        } catch {
            // an error was thrown
        }
        
        /// self .testAssert()
        self.testPreconditions()
    }
    
    /// 前置条件语句，作用类似断言
    func testPreconditions() {
        let index = 1
        precondition(index > 0, "Index must be greater than zero.")
    }
    
    /// 断言
    func testAssert() {
        let age = -3
        /// 判断等式是否成立，不成立时会打印后面的描述信息并终止程序运行
        assert(age >= 0, "A person's age can't be less than zero.")
    }
    
    /// 捕捉异常
    func throwAnError() throws {
        let arr:NSArray = NSArray()
        print(arr.firstObject!)
    }
    
    /// 可选类型
    func testOptional() {
        /// 可选类型在定义时，在类型后面添加‘？’，用以表明该对象可能为空
        /// 在使用可选类型对象时，可以通过强制解包(unwarp)用以表明使用该对象时确认其不为空
        
        let possibleString:String? = "An optional string"
        let forcedString:String = possibleString!
        print(forcedString)
        
        let assumedString:String! = "An implicitly unwarpped optional string"
        let implicitString:String = assumedString
        print(implicitString)
    }
    
    /// 元组的使用
    func testTuples() {
        let http404Error = (404,"Not found")
        let (statusCode,statusMsg) = http404Error
        print("The statusCode is \(statusCode),the error message is \(statusMsg)")
        
        /// or
        print("The statusCode is \(http404Error.0),the error message is \(http404Error.1)")
        
        /// or
        let (justStatusCode,_) = http404Error
        print("The status code is \(justStatusCode)")
        
        /// or
        let http200Status = (statusCode:200,description:"OK")
        print("The code is \(http200Status.statusCode),the message is \(http200Status.description)")
    }
    
    /// 布尔类型的使用及注意事项
    func testBool(isTrue:Bool) {
        if isTrue {
            print("isTrue")
        } else {
            print("isFalse")
        }
        
        // 下面是错误的分支判断方法(Object C 语法内可以使用此方式)
//        let i = 1
//        if i {
//            print("is an error syntax")
//        }
        
        // 如果要通过非布尔类型的数据进行分支判断，则应使用恒等式进行判断，如下：
        let j = 1
        if j == 1 {
            print("j equal 1")
        }
    }
    
    /// 类型替换
    func testTypealias() {
        typealias DJUInt8 = UInt8
        print("The max of UInt8 is \(DJUInt8.max),the min of that is \(DJUInt8.min)")
    }
    
    /// 特殊字符
    func specialString() {
        let cat = "🐱"
        print(cat)
    }
    
    /// 不带参数无返回值的函数
    func testNoParams() {
        var str:String = ""
        str = "1" + "2" /// 字符串拼接
        print(str)
        print("str === \(str)")
    }
    
    /// 带参数及返回值的函数
    func test1(str:String) -> String {
        
        return str
    }
}