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Kotlin vx Swift

Comparing Null-Safe Languages Swift and Kotlin

Null Safetyな言語 Kotlin と Swift を比較

Objective-Cの代替えとしてアップルで生まれたプログラミング言語 Swift と Javaや PHPなどの統合開発環境(IDE)を作っている JetBrainsで生まれたプログラミング言語 Kotlin比較してみます。

Swiftは iOSやmacOS、Kotlinは Android の開発用言語として利用されています。今どきのプログラミング言語の特徴である、Null Safety、クロージャ、継承といった機能を持っています。

基本

いつのもメッセージ

Swift
Kotlin
 
print("Hello, world!")
 
println("Hello, world!")

定数と変数

Swift
Kotlin
 
let myConstant = 36
var myVariable = 36
myVariable = 43
 
val myConstant = 36
var myVariable = 36
myVariable = 43

明示的に型を指定

Swift
Kotlin
 
let explicitDouble: Double = 63.8
 
val explicitDouble: Double = 63.8

型変換

Swift
Kotlin
 
let label = "幅 "
let width = 120
let widthLabel = label + String(width)
 
val label = "幅 "
val width = 120
val widthLabel = label + width
 
let cars = 3
let ships = 4
let vehicle = "乗り物 \(cars+ships) " + "台"
 
val cars = 3
val ships = 4
val vehicle = "乗り物 ${cars+ships} " + "台"

制御

Swift
Kotlin
 
if score > 75 {
    println("よくできました")
} else {
    println("がんばりましょう")
}
 
if (score > 75) {
    println("よくできました")
} else {
    println("がんばりましょう")
}
 
for item in array {
    print(item)
}
 
for (item in array) {
    println(item)
}
 
for i in 1..<5 {
    print(i)
}
 
for (i in 1..4) {
    println(i)
}
 
while num < total {
    
}
 
while (num < total) {
    
}
 
switch numberSymbol {
case "一":
    print("いち")
case "二":
    print("に")
case "三":
    print("さん")
default:
    print("いくつ？")
}
 
when (numberSymbol) {
    "一" -> println("いち")
    "二" -> println("に")
    "三" -> println("さん")
    else -> {
        println("いくつ？")
    }
}

Null Safety (Type safe)

Optional と Nullable

Swift
Kotlin
 
var name: String?
 
var name: String?
 
if let aName = name {
    print("name is \(aName.count) chars")
} else {
    print("name is nil")
}
 
if (name != null) {
    println("name is %d chars".format(name.length))
} else {
    println("name is null")
}
 
let count = name?.count
 
val length = name?.length
 
let aName = name ?? "Swift"
 
val aName = name ?: "Kotlin"
 
let count = name!.count
 
val length = name!!.length

Collections

Arrays

Swift
Kotlin
 
var shoppingList = [
    "おにぎり",
    "お茶",
    "チョコレート",
    "エクレア"
]
shoppingList[1] = "紅茶"
 
val shoppingList = arrayOf(
    "おにぎり",
    "お茶",
    "チョコレート",
    "エクレア"
)
shoppingList[1] = "紅茶"

Maps

Swift
Kotlin
 
var os = [
    "Mac OS X": "Apple",
    "Windows":  "Microsoft"
]
os["Solaris"] = "Sun"
 
val os = mutableMapOf(
    "Mac OS X" to "Apple",
    "Windows"  to "Microsoft"
)
os("Solaris") = "Sun"

空

Swift
Kotlin
 
let emptyArray = [String]()
let emptyDictionary = [String: Float]()
 
val emptyArray = arrayOf()
mapOf()

関数

関数

Swift
Kotlin
 
func yourName(given: String, family: String) -> String {
    return "\(family)家の \(given)"
}
yourName("太郎", "桃宮")
 
fun yourName(given: String, family: String): String {
    return "${family}家の $given"
}
yourName("太郎", "桃宮")

タプルを返す関数

Swift
Kotlin
 
func getPrices() -> (Double, Double, Double) {
    return (12.74, 3.85, 9.17)
}
 
data class Prices(val a: Double, val b: Double, val c: Double)
fun getPrices() = Prices(12.74, 3.85, 9.17)

可変引数

Swift
Kotlin
 
func sumOf(_ numbers: Int...) -> Int {
    var sum = 0
    for number in numbers {
        sum += number
    }
    return sum
}
sumOf(36, 138, 65, 11)
 
fun sumOf(vararg numbers: Int): Int {
    var sum = 0
    for (number in numbers) {
        sum += number
    }
    return sum
}
sumOf(36, 138, 65, 11)

デフォルト引数

Swift
Kotlin
 
func join(str1: String, str2: String, joiner: String = " ") -> String {
    return str1 + joiner + str2
}
 
fun join(str1: String, str2: String, joiner: String = " "): String {
    return str1 + joiner + str2
}

名前付き引数

Swift
Kotlin
 
func area(width: Double, height: Double) -> Double {
    return width * height
}

area(width: 120, height: 80)
 
fun area(width: Double, height: Double) = width * height



area(width = 120, height = 80)

関数型

Swift
Kotlin
 
func makeIncrementer() -> (Int -> Int) {
    func addOne(number: Int) -> Int {
        return number + 1
    }
    return addOne
}
let increment = makeIncrementer()
increment(7)
 
fun makeIncrementer(): (Int) -> Int {
    val addOne = fun(number: Int): Int {
        return number + 1
    }
    return addOne
}
val increment = makeIncrementer()
increment(7)

Map

Swift
Kotlin
 
let numbers = [18, 14, 7, 25]
numbers.map { 2 * $0 }
 
val numbers = listOf(18, 14, 7, 25)
numbers.map { 2 * it }

Sort

Swift
Kotlin
 
var mutArray = [1, 11, 5, 3, 7, 2]
mutArray.sort()
 
listOf(1, 11, 5, 3, 7, 2).sorted()

クラス

クラス定義

Swift
Kotlin
 
class Shape {
    var numberOfSides = 0
    func feature() -> String {
        return "辺の数：\(numberOfSides)"
    }
}
 
class Shape {
    var numberOfSides = 0
    fun feature() = "辺の数：$numberOfSides"
}

インスタンス

Swift
Kotlin
 
var shape = Shape()
shape.numberOfSides = 5
var shapeDescription = shape.feature()
 
var shape = Shape()
shape.numberOfSides = 5
var shapeDescription = shape.feature()

継承

Swift
Kotlin
 
class ShapeBase {
    var numberOfSides: Int = 0
    let name: String

    init(name: String) {
        self.name = name
    }

    func feature() -> String {
        return "辺の数：\(numberOfSides)"
    }
}

class Square: ShapeBase {
    var sideLength: Double

    init(sideLength: Double, name: String) {
        super.init(name: name)
        self.sideLength = sideLength
        self.numberOfSides = 4
    }

    func area() -> Double {
        return sideLength * sideLength
    }

    override func feature() -> String {
        return "\(name)の辺の数：\(numberOfSides)"
    }
}

let rectangle = Square(sideLength: 16.2, name: "正方形")
rectangle.area()
rectangle.feature()
 
open class ShapeBase(val name: String) {
    var numberOfSides = 0

    open fun feature() = "辺の数： $numberOfSides."
}

class Square(var sideLength: BigDecimal, name: String) : ShapeBase(name) {
    init {
        numberOfSides = 4
    }

    fun area() = sideLength.pow(2)

    override fun feature() = "${name}の辺の数：$sideLength"
}

val rectangle = Square(BigDecimal("16.2"), "正方形")
rectangle.area()
rectangle.feature()

型チェック

Swift
Kotlin
 
var carCount = 0
var shipCount = 0
 
for item in vehicle {
    if item is Car {
        carCount += 1
    } else if item is Ship {
        shipCount += 1
    }
}
 
var carCount = 0
var shipCount = 0
 
for (item in vehicle) {
    if (item is Car) {
        carCount++
    } else if (item is Ship) {
        shipCount++
    }
}

キャスト

Swift
Kotlin
 
for vehicle in Vehicle {
    if let car = vehicle as? Car  {
        print("種類: \(car.type)")
    }
}
 
for (vehicle in Vehicle) {
    if (vehicle is Car) {
        print("種類: ${vehicle.type}")
    }
}

Protocol / Interface

Swift
Kotlin
 
protocol Nameable {
    func name() -> String
}

func f<T: Nameable>(x: T) {
    print("名前： " + x.name())
}
 
interface Nameable {
    fun name(): String
}

fun f<T: Nameable>(x: T) {
    println("名前： " + x.name())
}

Extensions

Swift
Kotlin
 
extension Double {
    var km: Double { return self * 1_000.0 }
    var m:  Double { return self }
    var cm: Double { return self / 100.0 }
    var mm: Double { return self / 1_000.0 }
    var ft: Double { return self / 3.28 }
}

let oneInch = 2.54.cm
print("1インチ ＝ \(oneInch) メートル")

let twoFeet = 2.ft
print("2フィート ＝ \(twoFeet) メートル")
 
val Double.km: Double get() = this * 1000
val Double.m: Double get() = this
val Double.cm: Double get() = this / 100
val Double.mm: Double get() = this / 1000
val Double.ft: Double get() = this / 3.28

val oneInch = 2.54.cm
println("1インチ ＝ $oneInch メートル")

val twoFeet = 2.0.ft
println("2フィート ＝ $twoFeet メートル")

プログラミング言語

  • Java
    Java
    write once, run anywhere
  • PHP
    PHP
    Hypertext Preprocessor
  • Ruby
    Ruby
    Ruby & Rails
  • Python
    Python
    Python is powerful... and fast
  • Swift
    Swift
    Protocol-oriented Programming
  • Kotlin
    Kotlin
    A modern programming language
  • C
    C
    C & C++ Language
  • Rust
    Rust
    borrow checker
  • Go
    Go
    fast, reliable, and efficient
  • LISP
    LISP
    Recursive, Lambda, S-Expression