Swift Error的处理方法说明

enum SomeError: Error {
    case illegalArg(String)
    case outOfBounds(Int, Int)
    case outOfMemory
}

func divide(_ num1: Int, _ num2: Int) throws -> Int {
    if num2 == 0 {
        throw SomeError.illegalArg("0不能作为除数")
    }
    return num1 / num2
}

func test() {
    do {
        try divide(20, 0)
    } catch let SomeError.illegalArg(msg) {
        print("参数异常：", msg)
    } catch let SomeError.outOfBounds(size, index) {
        print("下标越界：", "size = \(size), index = \(index)")
    } catch SomeError.outOfMemory {
        print("内存溢出")
    } catch {
        print("其他错误")
    }
}

func test() throws {
    print(try divide(200, 0))
}

func test() throws {
    do {
        print(try divide(200, 0))
    } catch let error as SomeError {
        print(error)
    }
}

func test() throws {
    do {
        print(try divide(200, 0))
    } catch is SomeError {
        print("SomeError")
    }
}

do {
    try divide(20, 0)
} catch let error {
    switch error {
    case let SomeError.illegalArg(msg):
        print("参数异常：", msg)
    default:
        print("其他异常")
    }
}

override func viewWillAppear(_ animated: Bool) {
    super.viewWillAppear(animated)
    try test0()
}
func test0() throws -> Void {
    try test1()
}
func test1() throws -> Void {
    try test2()
}
func test2() throws -> Void {
    do {
        print(try divide(200, 0))
    } catch is SomeError {
        print("This is SomeError")
    }
}

func test() -> Void {
    print("1")
    var result1 = try? divide(20, 10) // Optional(2), Int?
    var result2 = try? divide(20, 0) // nil
    var result3 = try! divide(20, 10) // 2, Int
    print("2")
}

var a = try? divide(20, 0)
var b: Int?
do {
    b = try divide(20, 0)
} catch {
    b = nil
}

func exec(_ fn: (Int, Int) throws -> Int, _ num1: Int, _ num2: Int) rethrows -> Void {
    print(try fn(num1, num2))
}

func open(_ filename: String) -> Int {
    print("open")
    return 1
}
func close(_ file: Int) -> Void {
    print("close")
}
func processFile(_ filename: String) throws -> Void {
    let file = open(filename)
    defer {
        close(file)
    }
    try divide(20, 0)
}

func fn1() -> Void {
    print("fn1")
}
func fn2() -> Void {
    print("fn2")
}
func testDefer() -> Void {
    defer {
        fn1()
    }
    defer {
        fn2()
    }
} //fn2 fn1