What’s New in Swift4.2 まとめ ref: https://qiita.com/hanawat/items/4605f9e357c8794b58d7

file0.txt

Apple Swift version 4.2 (swiftlang-1000.0.16.7 clang-1000.10.25.3)

file1.swift

// Swift4.1
protocol Bachelor {
    func givesRose()
}

extension Array: Bachelor where Element: Bachelor {
    func givesRose() { forEach { $0.givesRose() } }
}

class Man: Bachelor {
    func givesRose() { print("🌹") }
}

let men = [Man(), Man()]
men.givesRose() // 🌹🌹

// Swift4.2
func dynamicallyBachelor(_ men: Any) {
    if let men = men as? Bachelor {
        men.givesRose()
    } else {
        fatalError("Swift4.1")
    }
}

dynamicallyBachelor(men) // 🌹🌹

file10.swift

let randomChar = "hello".randomElement() // Random character
let randomFruit = ["apple", "orange", "banana"].randomElement() // Random string

file11.swift

let shuffledChar = "hello".shuffled() // Shuffled character
var fruits = ["apple", "orange", "banana"]
fruits.shuffle() // Shuffled array

file12.swift

/// Mimicking the old random function.
struct OldRandomNumberGenerator: RandomNumberGenerator {
    mutating func next() -> UInt64 {
        return UInt64(arc4random_uniform(.max))
    }
}

var oldGenerator = OldRandomNumberGenerator()
let oldRandomInt = Int.random(in: 0...10, using: &generator) // 1-10 random number

file13.swift

let range = 0...9
let isEven: (Int) -> Bool = { $0 % 2 == 0 }
let lastEven = range.last(where: isEven) // 8
let lastEvenIndex = range.lastIndex(where: isEven) // inRange(8)

file14.swift

// Swift4.1
struct GridPoint {
    var x: Int
    var y: Int
}

extension GridPoint: Hashable {
    var hashValue: Int {
        return x.hashValue ^ y.hashValue &* 16777619
    }

    static func == (lhs: GridPoint, rhs: GridPoint) -> Bool {
        return lhs.x == rhs.x && lhs.y == rhs.y
    }
}

file15.swift

// swift4.2
struct GridPoint {
    var x: Int
    var y: Int
}

extension GridPoint: Hashable {
    func hash(into hasher: inout Hasher) {
        hasher.combine(x)
        hasher.combine(y)
    }

    static func == (lhs: GridPoint, rhs: GridPoint) -> Bool {
        return lhs.x == rhs.x && lhs.y == rhs.y
    }
}

file16.swift

let range = 0...9
// Swift4.1
let isSmallerThanTen = !range.contains(where: { $0 >= 10 }) // true
// Swift4.2
let isSmallerThanTen = range.allSatisfy({ $0 < 10 }) // true

file17.swift

struct GridPoint {
    var x: Int // Offset: 0
    var y: Int // Offset: 8
}

let offset = MemoryLayout<GridPoint>.offset(of: \GridPoint.y) // 8

file2.swift

enum Fruit: CaseIterable {
    case apple
    case orange
    case banana
}

Fruit.allCases // [apple, orange, banana]

file3.swift

// error: type 'Fruit' does not conform to protocol 'CaseIterable'
enum Fruit: CaseIterable {
    case apple(Int)
}

file4.swift

@dynamicMemberLookup
struct Response {
    private var raw = ["foo": "foo", "baz": "baz"]
    subscript(dynamicMember name: String) -> String? {
        get { return raw[name] }
        set { raw[name] = newValue }
    }
}

var response = Response()
response.foo // foo
response.bar // nil
response.bar = "bar"
response.bar // bar

file5.swift

func doSomething() {
    #warning("TODO: Implement logic.")
}

if canImport(UIKit)
    // Do something.
#else
    #error("Requires UIKit.")
#endif

file6.swift

var faces = ["😀", "😭", "😄"]
faces.removeAll(where: { $0 == "😭" }) // ["😀", "😄"]

file7.swift

let x: UInt16 = 0xabcd
let (firstByte, secondByte) = withUnsafeBytes(of: x, { pointer in
    return (pointer[0], pointer[1])
})

String(firstByte, radix: 16) // cd
String(secondByte, radix: 16) // ab

file8.swift

var flag = false
// Swift4.1
// flag = !flag
// Swift4.2
flag.toggle() // true

file9.swift

let randomInt = Int.random(in: 1...10) // 1-10 random number
let randomInt32 = Int32.random(in: .min ... .max) // Int.min-.max random number
let randomDouble = Double.random(in: 0.0..<1.0) // 0.0-1.0 random number
let randomBool = Bool.random() // true or false