クロージャ

はじめに

メモリ管理

クロージャの種類

クロージャの構文

補足

クロージャの構文

{ (parameters) -> return type in
    statements
}


func backward(_ s1: String, _ s2: String) -> Bool {
    return s1 > s2
}
//If we didn't use closures, our code structure would be as follows.

var reversedNames = names.sorted(by: backward)

クロージャの構文

let names = ["Chris", "Alex", "Ewa", "Barry", "Daniella"]
let reversedNames = names.sorted(by: { (s1: String, s2: String) -> Bool in
    return s1 > s2
})

print(reversedNames)

///sorted method takes closure as parameter.

inキーワード

コンテキストから型を推論する

例

let names = ["Chris", "Alex", "Ewa", "Barry", "Daniella"]
let reversedNames = names.sorted(by: { (s1: String, s2: String) -> Bool in
    return s1 > s2
})

print(reversedNames)

短縮構文

/*
In this example, the return keyword has been extracted.
It already has single expression. 
There is no need to express it as an extra with return.
*/

var names = ["Coddy", "Kit"]
let reversedNames = names.sorted(by: { s1, s2 in s1 > s2 } )
print(reversedNames)

例

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

名前の短縮記法

let names = ["Coddy", "Kit"]
let reversedNames = names.sorted(by: { $0 > $1 } )
print(reversedNames)

// In this example $0 will shortcut the first parameter and $1 will shortcut the second parameter.

例の短縮

var names = ["Coddy", "Kit"]

let reversedNames = names.sorted(by: >)
print(reversedNames)
// Greater than operator takes two parameters and the rotation type is squat.

トレーリングクロージャ

最後のパラメータ

class Animator {
    class func animate(withDuration duration: Double, animations: () -> Void) {
        animations()
    }
}

class MyViewController {
    func start() {
        // With the traditional method, we can call this fund as follows.
        Animator.animate(withDuration: 1, animations: { [unowned self] in
            print("red")
        })
    }
}
MyViewController().start()

上のコードは読みにくいため、次のように記述できます

import Foundation
Thread.sleep(forTimeInterval: 1)
print("Background color changed to red")

例

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
}

構文

/*
In the example below, animations
are expressed as closure.
*/
public class func animate(withDuration: TimeInterval, animations: () -> Void)

// In traditional usage, we need to make a call like the following.
UIView.animate(withDuration: 1, animations: { [unowned self] in
    self.view.backgroundColor = UIColor.red
})

/*
In this way, both the readability of the code
increases and we avoid the use of extra brackets.
If it is as above and the last parameter of the method 
is closure, Swift allows to make a call like the one below.
*/

UIView.animate(withDuration: 1) { [unowned self] in
    self.view.backgroundColor = UIColor.red
}

以下のコードを使ってコードをテストできます

func greetThenRunClosure(name: String, closure: () -> ()) {
    print("Hello, \(name)!")
    closure()
}

greetThenRunClosure(name: "Paul") {
    print("The closure was run")
}

クロージャによる値のキャプチャ

続き

func makeIncrementer(forIncrement amount: Int) -> () -> Int {
    var runningTotal = 0
    func incrementer() -> Int {
        runningTotal += amount
        return runningTotal
    }
    return incrementer
}

let incrementByTen = makeIncrementer(forIncrement: 10)

print(incrementByTen())
// returns a value of 10
print(incrementByTen())
// returns a value of 20
print(incrementByTen())
// returns a value of 30

続き

警告

@escaping

@ESCAPINGキーワード

nonEscaping

エスケーピングクロージャの使用

おめでとうございます