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Swift vs Scala

Swift and Scala are similar, aren't they?

Swift と Scalaって似てない？

アップルのiOSおよびOS Xのためのプログラミング言語 Swift と オブジェクト指向言語と関数型言語の特徴を統合したプログラミング言語 Scala がとても 似ているのでちょっと比較してみます。比較だけしているので、それぞれの細かい言語仕様は各サイトで確認して下さい。

Scala は、もっと簡単な（省略した）記述ができますが、Swiftとの比較を分かりやすくするためにちょっと冗長な記述にしています。

※ 初期のバージョンのSwiftをもとに記述しています。最新のバージョンの Swiftでは、一部記述方法が変更されています。

基本

いつのもメッセージ

Swift
Scala
 
println("Hello, world!")
 
println("Hello, world!")

定数と変数

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

型変換

Swift
Scala
 
let label = "幅 "
let width = 120
let widthLabel = label + String(width)
 
val label = "幅 "
val width = 120
val widthLabel = label + width

制御

Swift
Scala
 
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 var index = 0; i < 3; ++index {
    println("index = \(index)")
}
 
ありません
 
ありません
 
for (i <- 1 to 5)
    yield i^2
 
while num < total {
    
}
 
while (num < total) {
    
}
 
switch numberSymbol {
case "一":
    println("いち")
case "二":
    println("に")
case "三":
    println("さん")
default:
    println("いくつ？")
}
 
numberSymbol match {
case "一" => println("いち")
case "二" => println("に")
case "三" => println("さん")
case _    => println("いくつ？")
}

インクリメンタル・ループ

Swift
Scala
 
let seasons = ["春", "夏", "秋", "冬"]
let count = seasons.count
for i in 0..count {
    println("\(seasons[i])")
}
 
val seasons = Array("春", "夏", "秋", "冬")
val count = seasons.length
for (i <- 0 until count) {
    println(s"${seasons(i)}")
}
 
for index in 1...3 {
    println("\(index) × 5 ＝ \(index * 5)")
}
// 1 × 5 ＝ 5
// 2 × 5 ＝ 10
// 3 × 5 ＝ 15
 
for (index <- 1 to 3) {
    println(s"$index × 5 ＝ ${index * 5}")
}
// 1 × 5 ＝ 5
// 2 × 5 ＝ 10
// 3 × 5 ＝ 15

式とCollections

式

Swift
Scala
 
a + b
 
a + b
 
a = b
(a, b) = (1, 2)
 
a = b
ありません
 
a is T
 
a.isInstanceOf[T]
 
a as T
a as? T
 
a.asInstanceOf[T]
ありません
 
"\(x) + \(y) = \(x + y)"
 
s"$x + $y = ${x + y}"
 
[a, b, c]
 
Array(a, b, c)
 
[a: b, c: d]
 
scala.collection.mutable.Map(a -> b, c -> d)
 
self
self.foo
self[foo]
self.init(foo)
 
this
this.foo
this(foo)
this(foo)
 
super.foo
super[foo]
super.init(foo)
 
super.foo
super(foo)
ありません

Arrays

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

Maps

Swift
Scala
 
var os = [
    "Mac OS X": "Apple",
    "Windows":  "Microsoft"
]
os["Solaris"] = "Sun"
 
var os = scala.collection.mutable.Map(
    "Mac OS X" -> "Apple",
    "Windows"  -> "Microsoft"
)
os("Solaris") = "Sun"

空

Swift
Scala
 
let emptyArray = String[]()
let emptyDictionary = Dictionary()
let emptyArrayNoType = []
 
val emptyArray = Array[String]()
val emptyDictionary = Map[String, Float]()
val emptyArrayNoType = Array()

closure

Swift
Scala
 
{ (parameters) -> returnType in
    ...
}
 
{ (parameters) =>
    ...
}

placeholders

Swift
Scala
 
f { $0 > $1 }
 
f { _ > _ }

関数

関数

Swift
Scala
 
func yourName(given: String, family: String) -> String {
    return "\(family)家の \(given)"
}
yourName("太郎", "桃宮")
 
def yourName(given: String, family: String): String = {
    return s"${family}家の $given"
}
yourName("太郎", "桃宮")

タプル

Swift
Scala
 
func getPrices() -> (Double, Double, Double) {
    return (12.74, 3.85, 9.17)
}
 
def getPrices(): (Double, Double, Double) = {
    return (12.74, 3.85, 9.17)
}

可変引数

Swift
Scala
 
func sumOf(numbers: Int...) -> Int {
    var sum = 0
    for number in numbers {
        sum += number
    }
    return sum
}
sumOf(36, 138, 65, 11)
 
def sumOf(numbers: Int*): Int = {
    var sum = 0
    for (number <- numbers) {
        sum += number
    }
    return sum
}
sumOf(36, 138, 65, 11)

デフォルト引数

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

名前付き引数

Swift
Scala
 
func area(#width: Int, #height: Int) -> Int {
    return width * height
}

area(width: 120, height: 80)
 
def area(width: Int, height: Int): Int = {
    return width * height
}

area(width = 120, height = 80)

関数型

Swift
Scala
 
func makeIncrementer() -> (Int -> Int) {
    func addOne(number: Int) -> Int {
        return 1 + number
    }
    return addOne
}
var increment = makeIncrementer()
increment(7)
 
def makeIncrementer(): Int => Int = {
    def addOne(number: Int): Int = {
        return 1 + number
    }
    return addOne
}
var increment = makeIncrementer()
increment(7)

Map

Swift
Scala
 
var numbers = [18, 14, 7, 25]
numbers.map({ number in 2 * number })
 
var numbers = Array(18, 14, 7, 25)
numbers.map( number => 2 * number )

Sort

Swift
Scala
 
sort([1, 11, 5, 3, 7, 2]) { $0 > $1 }
 
Array(1, 11, 5, 3, 7, 2).sortWith(_ > _)

クラス

クラス定義

Swift
Scala
 
class Shape {
    var numberOfSides = 0
    func simpleDescription() -> String {
        return "辺の数： \(numberOfSides) "
    }
}
 
class Shape {
    var numberOfSides = 0
    def simpleDescription(): String = {
        return s"辺の数： $numberOfSides"
    }
}

インスタンス

Swift
Scala
 
var shape = Shape()
shape.numberOfSides = 5
var shapeDescription = shape.simpleDescription()
 
var shape = new Shape()
shape.numberOfSides = 5
var shapeDescription = shape.simpleDescription()

型チェック

Swift
Scala
 
var carCount = 0
var shipCount = 0
 
for item in vehicle {
    if item is Car {
        ++carCount
    } else if item is Ship {
        ++shipCount
    }
}
 
var carCount = 0
var shipCount = 0
 
for (item <- vehicle) {
    if (item.isInstanceOf[Car]) {
        carCount += 1
    } else if (item.isInstanceOf[Ship]) {
        shipCount += 1
    }
}

パターンマッチ

Swift
Scala
 
var carCount = 0
var shipCount = 0

for item in vehicle {
  switch item {
    case let car as Car:
      ++carCount
      println("車: '\(car.name)'")
    case let ship as Ship:
      ++shipCount
      println("船: '\(ship.title)'")
  }
}
 
var carCount = 0
var shipCount = 0

for (item <- vehicle) {
  item match {
    case car: Car =>
      carCount += 1
      println(s"車: '${car.name}'")
    case ship: Ship =>
      shipCount += 1
      println(s"船: '${ship.title}'")
  }
}

キャスト

Swift
Scala
 
for object in someObjects {
    let vehicle = object as Vehicle
    println("乗り物: '\(vehicle.name)'")
}
 
for (obj <- someObjects) {
    val vehicle = obj.asInstanceOf[Vehicle]
    println(s"乗り物: '${vehicle.name}'")
}

Protocol

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

func f<T: Nameable>(x: T) {
    println("名前： " + x.name())
}
 
trait Nameable {
    def name(): String
}

def f[T <: Nameable](x: T) = {
    println("名前： " + x.name())
}

Extensions

Swift
Scala
 
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
println("1インチ ＝ \(oneInch) メートル")

let twoFeet = 2.ft
println("2フィート ＝ \(twoFeet) メートル")
 
object Extensions {
    implicit class DoubleUnit(d: Double) {
        def km: Double = { return d * 1000.0 }
        def m:  Double = { return d }
        def cm: Double = { return d / 100.0 }
        def mm: Double = { return d / 1000.0 }
        def ft: Double = { return d / 3.28 }
    }
}
import Extensions.DoubleUnit

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

val twoFeet = 2.ft
println(s"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