swift中闭包的使用

{(parameters) -> return type in
   statements
}

//let append = {(str1 aa:String,Str2 bb: String)-> String in 报错，闭包没有外部参数名
let append = {(str1:String,Str2: String)-> String in
  print("\(str1)------\(Str2)")//20------30
    return "\(str1)\(Str2)"//2030
}
//print(append(str1:"20",str2:"30")) 报错，闭包里面不用传参数名
print(append("20","30"))//2030

let append: ( String, String) -> String = {
    (str1, str2) in return str1 + str2
}
print(append("one", "two"))//onetwo

//无参有反  可以直接省略 "in"  如果加上in，这里会报错
let test: () -> String = {
    return "test闭包"
}
print(test())//test闭包

let test: () -> Void = {
    print("test闭包")//输出：test闭包
}
test()

func showYouTest(testBlock: @escaping () -> Void) {
    //做一个延迟操作
    DispatchQueue.main.asyncAfter(deadline: DispatchTime.now() + 5) {
        //五秒之后调用闭包
        testBlock()
    }
    print("我是函数")
}

showYouTest {
   print("11111111111111111111")//5秒后执行这里
}