总结：整个Closure的作用在于简化语言表述形式。
一、闭包的简化
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: >)
二、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
- }
闭包的实现在函数参数列表外；
再次精简
reversedNames = names.sorted() { $0 > $1 }
reversedNames = names.sorted { $0 > $1 }
完全移出
- 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!"