一. try catch

enum ErrorEnum : Error {
    case errorString(String)
}


func chuFa(_ num1: Int, _ num2: Int)throws -> Int{
    if num2 == 0 {
        throw ErrorEnum.errorString("被除数不能为0")
    }
    return num1/num2
}

//好几种写法
do {
    let ret = try chuFa(10, 0)
    print(ret)
} catch let ErrorEnum.errorString(errorMsg){
    print(errorMsg)
} catch {
    print("其他异常")
}

do {
    let ret = try chuFa(10, 0)
    print(ret)
} catch let error as ErrorEnum{
    print(error)
} catch {
    print("其他异常")
}

do {
    let ret = try chuFa(10, 0)
    print(ret)
} catch is ErrorEnum{
    print("ErrorEnum")
} catch {
    print("其他异常")
}

do {
    let ret = try chuFa(10, 0)
    print(ret)
} catch let error{
    switch error {
    case let ErrorEnum.errorString(str):
        print(str)
    default:
        print("其他类型的异常")
    }
} catch {
    print("其他异常")
}


try chuFa(10, 0)    //errorString : "被除数不能为0"
try? chuFa(10, 0)   //nil  -> try? 抛出错误, 返回nil
//try! chuFa(10, 0) //崩溃  -> try! 抛出错误不处理的话,会崩溃

var bbbbb: Int?
do {
    bbbbb = try chuFa(10, 0)
} catch {
    bbbbb = nil
}

// throws   代表函数可能会抛出异常
// rethrows 函数本身不会抛出异常,但调用闭包参数抛出异常,那么它会将异常往上抛
//rethrows  和throws差不多

二. refer

//: # defer
// defer  美[dɪˈfɜːr]    v.延期，推迟；听从，遵从（defer to）
// 用来定义以任何方式(抛错误 return等)离开代码块前必须执行的代码
// defer语句将延迟到当前作用域结束之前执行

print("-------------------------------------------------------------------------------------------")
func chuFa_1(_ num1: Int, _ num2: Int)throws -> Int{
    print("进入到chufa_1")
    if num2 == 0 {
        throw ErrorEnum.errorString("被除数不能为0")
    }
    return num1/num2
}
var aaa: Int?
do {
    defer{
        print("666")
    }
    aaa = try chuFa_1(10, 0)
} catch let ErrorEnum.errorString(errMsg){
    aaa = nil
    print(errMsg)
}

/*
 进入到chufa_1
 666
 被除数不能为0
 */
//解释: 虽然 print("666")这句话 在最上面,但是先不执行, 而是当前作用域结束之前执行