什么是封包？ (What is Closure?)

Closures are self-contained blocks of functionality that can be passed around and used in your code. Closures in Swift are similar to blocks in C and Objective-C and to lambdas in other programming languages.

闭包是独立的功能块，可以在代码中传递和使用。 Swift中的闭包类似于C和Objective-C中的块以及其他编程语言中的lambda。

swift.org

swift.org

• Closure is a function and “func” keyword

  闭包是函数和“ func ”关键字

• Closure is a block of code that you can assign to a variable.闭包是可以分配给变量的代码块。

• In Swift Variables “var” and Constants “let” store information, Functions “func” execute tasks and Closures have a function code in form of a variable and can be passed around.

  在Swift变量“ var ”和常量“ let ”中存储信息，函数“ func ”执行任务，闭包具有变量形式的函数代码，并且可以传递。

封闭的类型有哪些？ (What are the types of the Closure?)

• Closure without niether parameters nor return value.不带任何参数或返回值的闭包。
• Closure that accepts parameters.接受参数的闭包。
• Closure returns value.闭包返回值。
• Trailing Closure尾随闭包

没有参数或返回值的闭包 (Closure without parameters or return value)

var myClosure = {    print("Hello I'm a Closure")}myClosure()         => Hello I'm a Closure

接受参数的闭包 (Closure that acceptes parameters)

var closure: (String) -> Void = { str in    print(str)}var closure: (Int, Int) -> Void = { first, second in    print(first + second)}

Since closures parameters don’t have names you can refer to them with $ + parameters number

由于闭包参数没有名称，因此可以使用$ +参数编号引用它们

var closure: (Int, Int) -> Void = {    print($0 + $1)}closure(3, 2)          => 5

闭包返回值 (Closure that returns values)

var closure: () -> String = {    return "Hello Closure"}var value = closure()print(value)  => Hello Closure

closures can also accept parameters and return value

闭包也可以接受参数和返回值

var addTwoNumbers: (Int, Int) -> Int = {    return $0 + $1}addTwoNumbers(4, 5)   => 9

尾随闭包 (Trailing Closure)

If the last parameter to a function is closure that’s called trailing closure

如果函数的最后一个参数是闭包，则称为尾随闭包

func callMe(closure: () -> Void) {    print("will call you")    closure()    print("did call you")}callMe {    print("calling you...")}=> will call you=> calling you...=> did call you

Another example of the trailing closure with parameter

带参数的尾随闭包的另一个示例

func callMe(name: String, closure: (String) -> Void) {    print("\(name) will call you")    closure(name)    print("\(name) did call you")}callMe(name: "Smith") { name in    print(name, "is calling you")}=> Smith will call you=> Smith is calling you=> Smith did call you

Trailing closure with parameter and returns value

带参数的尾随闭包并返回值

func callMe(name: String, closure: (String) -> String) -> String {    return closure(name)}var whoIsCalling = callMe(name: "Smith") { (name) -> String in    return name}print(whoIsCalling)=> Smith is calling.