swift語言點評四-Closure

總結：整個Closure的做用在於簡化語言表述形式。

 

1、閉包的簡化

 

Closure expression syntax has the following general form:

 

• { () -> 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. 

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

 

Implicit Returns from Single-Expression Closures

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

 

Shorthand Argument Names

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.

 

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

 

Operator Methods

reversedNames = names.sorted(by: >)

 

 

2、拖尾變換

• 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
• }

 

閉包的實如今函數參數列表外；

 

再次精簡

 

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

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

 

 

 

徹底移出

• 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

異步解決方案

 

Autoclosures

表達式語句

• // 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!"