swift中闭包(closure)

下面是一个基本的闭包：

var multiplyClosure = { (a: Int, b: Int) -> Int in

return a * b

}

这就是一个基本的闭包类型，其基本格式为｛ （参数列表）-> 返回值 in 函数体｝

对上面这个闭包，可以进行如下的精减

1、去掉return

var multiplyClosure = { (a: Int, b: Int) -> Int in

a * b

}

2、去掉返回值类型，让系统自己推断

var multiplyClosure = { (a: Int, b: Int) in

a * b

}

3、将参数中的类型声明去掉，这种情况要实现声明变量的类型为闭包

var multiplyClosure: (Int,Int) -> Int

multiplyClosure = { (a, b) in

a * b

}

4、最后还可以将参数列表去掉，根据参数出现的位置来处理

var multiplyClosure: (Int,Int) -> Int

multiplyClosure = {

$0 * $1

}

声明一个没有参数和返回值的闭包

let voidClosure: () -> Void = {

print("Swift is awesome")

}

voidClosure()

下面这个是闭包作为返回值的一个例子

func countingClosure() -> (() -> Int) {

print("ok")

var counter = 0

let incrementCounter: () -> Int = {

print(counter)

counter += 1

print(counter)

return counter

}

return incrementCounter

}

let counter1 = countingClosure()

let counter2 = countingClosure()

//counter1时一个闭包，闭包作为函数执行，返回int类型的值

counter1()

counter1()

counter2()

一个例子：

func mathSum(times: Int, operation: (Int) -> Int) -> Int {

var result = 0

for i in 1...times {

result += operation(i)

}

return result

}

var result1 = mathSum(10, operation: {(a: Int) -> Int in return a * a })

print(result1)

var result2 = mathSum(10, operation: {(a: Int) -> Int in fibonacci(a)})

print(result2)