swift语言点评四-Closure

时间 2019-11-11

标签 swift 语言点评 closure 栏目 Swift 繁體版

原文原文链接

总结：整个Closure的做用在于简化语言表述形式。git

1、闭包的简化express

Closure expression syntax has the following general form:api

{ () -> in
}

reversedNames = names.sorted(by: { (s1: String, s2: String) -> Bool in
return s1 > s2
})

Because the sorting closure is passed as an argument to a method, Swift can infer the types of its parameters and the type of the value it returns. 闭包

reversedNames = names.sorted(by: { s1, s2 in return s1 > s2 } )异步

Implicit Returns from Single-Expression Closureside

reversedNames = names.sorted(by: { s1, s2 in s1 > s2 } )函数

Shorthand Argument Namesthis

Swift automatically provides shorthand argument names to inline closures, which can be used to refer to the values of the closure’s arguments by the names $0, $1, $2, and so on.orm

reversedNames = names.sorted(by: { $0 > $1 } )ci

Operator Methods

reversedNames = names.sorted(by: >)

2、拖尾变换

func someFunctionThatTakesAClosure(closure: () -> Void) {
// function body goes here
}
// Here's how you call this function without using a trailing closure:
someFunctionThatTakesAClosure(closure: {
// closure's body goes here
})
// Here's how you call this function with a trailing closure instead:
someFunctionThatTakesAClosure() {
// trailing closure's body goes here
}

闭包的实如今函数参数列表外；

再次精简

reversedNames = names.sorted() { $0 > $1 }

reversedNames = names.sorted { $0 > $1 }

彻底移出

let strings = numbers.map { (number) -> String in
var number = number
var output = ""
repeat {
output = digitNames[number % 10]! + output
number /= 10
} while number > 0
return output
}

Closures Are Reference Types

Whenever you assign a function or a closure to a constant or a variable, you are actually setting that constant or variable to be a reference to the function or closure.

Escaping Closures

异步解决方案

Autoclosures

表达式语句

// customersInLine is ["Ewa", "Barry", "Daniella"]
func serve(customer customerProvider: @autoclosure () -> String) {
print("Now serving \(customerProvider())!")
}
serve(customer: customersInLine.remove(at: 0))
// Prints "Now serving Ewa!"