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SWIFT 类似 SCALA

SWIFT 类似 SCALA

作者: amor_2018 | 来源:发表于2020-01-10 21:43 被阅读0次

    各个编程语言都有类似的地方,我们只要精通一门语言,就可以对比着学习,要不了多久就可以精通另一门语言,在网上看到Swift语言和Scala语言的对比,我们就来看看他们之间的一些相似之处。

    在WWDC 14上,苹果公司发布了一门新的编程语言Swift。这里有一个Swift和Scala的源代码对比,使用的是苹果公司在iTunes商店出版的《Swift编程语言》一书中的例子

    我猜测这两者是相关的,从语法上讲,Swift是Scala的一种方言。Swift从Scala继承了苹果列出的大部分标志性特性:类型推断、闭包、元组、协议、扩展、泛型、读取-执行-打印-循环(Read-Eval-Print-Loop)等等。

    尽管它们的语法相似,Swift的运行时环境与Scala的截然不同,这可能是新语言最有趣的地方。Scala编译到JVM,使用垃圾收集,它的对象模型透明地与Java集成。Swift编译为本机代码,使用自动引用计数,其对象模型透明地与Objective-C集成。因此,这两种语言之间的相似性并没有延伸到表面之下。

    Den Shabalin 提供了另一个优秀的 逐点比较.

    p.s. 不要把这段代码看得太严重!大部分都是死记硬背,简化了苹果给出的快速例子。我给出了一些更符合Scala习惯用法的翻译。如果您发现任何令人难以忍受的问题,请随时提交GitHub问题/拉请求。

    基础

    Hello World

    SWIFT

    println("Hello, world!")
    

    SCALA

    println("Hello, world!")
    

    变量和常量

    SWIFT

    var myVariable = 42
    myVariable = 50
    let myConstant = 42
    

    SCALA

    var myVariable = 42
    myVariable = 50
    val myConstant = 42
    

    显式类型

    SWIFT

    let explicitDouble: Double = 70
    

    SCALA

    val explicitDouble: Double = 70
    

    强制类型转换

    SWIFT

    let label = "The width is "
    let width = 94
    let widthLabel = label + String(width)
    

    SCALA

    val label = "The width is "
    val width = 94
    val widthLabel = label + width
    

    字符串插值

    SWIFT

    let apples = 3
    let oranges = 5
    let fruitSummary = "I have \(apples + oranges) " + 
                       "pieces of fruit."
    

    SCALA

    val apples = 3
    val oranges = 5
    val fruitSummary = s"I have ${apples + oranges} " +
                       " pieces of fruit."
    

    半开区间运算符 (Range Operator)

    SWIFT

    let names = ["Anna", "Alex", "Brian", "Jack"]
    let count = names.count
    for i in 0..count {
        println("Person \(i + 1) is called \(names[i])")
    }
    // Person 1 is called Anna
    // Person 2 is called Alex
    // Person 3 is called Brian
    // Person 4 is called Jack
    

    SCALA

    val names = Array("Anna", "Alex", "Brian", "Jack")
    val count = names.length
    for (i <- 0 until count) {
        println(s"Person ${i + 1} is called ${names(i)}")
    }
    // Person 1 is called Anna
    // Person 2 is called Alex
    // Person 3 is called Brian
    // Person 4 is called Jack
    

    闭区间运算符(Inclusive Range Operator)

    SWIFT

    for index in 1...5 {
        println("\(index) times 5 is \(index * 5)")
    }
    // 1 times 5 is 5
    // 2 times 5 is 10
    // 3 times 5 is 15
    // 4 times 5 is 20
    // 5 times 5 is 25
    

    SCALA

    for (index <- 1 to 5) {
        println(s"$index times 5 is ${index * 5}")
    }
    // 1 times 5 is 5
    // 2 times 5 is 10
    // 3 times 5 is 15
    // 4 times 5 is 20
    // 5 times 5 is 25
    

    集合

    数组/列表(Arrays)

    SWIFT

    var shoppingList = ["catfish", "water",
        "tulips", "blue paint"]
    shoppingList[1] = "bottle of water"
    

    SCALA

    var shoppingList = Array("catfish",
        "water", "tulips", "blue paint")
    shoppingList(1) = "bottle of water"
    

    映射 Maps

    SWIFT

    var occupations = [
        "Malcolm": "Captain",
        "Kaylee": "Mechanic",
    ]
    occupations["Jayne"] = "Public Relations"
    

    SCALA

    var occupations = scala.collection.mutable.Map(
        "Malcolm" -> "Captain",
        "Kaylee" -> "Mechanic"
    )
    occupations("Jayne") = "Public Relations"
    

    Empty Collections 空集合

    SWIFT

    let emptyArray = String[]()
    let emptyDictionary = Dictionary<String, Float>()
    let emptyArrayNoType = []
    

    SCALA

    val emptyArray = Array[String]()
    val emptyDictionary = Map[String, Float]()
    val emptyArrayNoType = Array()
    

    函数

    Functions 函数

    SWIFT

    func greet(name: String, day: String) -> String {
        return "Hello \(name), today is \(day)."
    }
    greet("Bob", "Tuesday")
    

    SCALA

    def greet(name: String, day: String): String = {
        return s"Hello $name, today is $day."
    }
    greet("Bob", "Tuesday")
    

    Scala 惯用法 (IDIOMATIC SCALA)

    def greet(name: String, day: String): String =
        s"Hello $name, today is $day."
    
    greet("Bob", "Tuesday")
    

    元组返回 Tuple Return

    SWIFT

    func getGasPrices() -> (Double, Double, Double) {
        return (3.59, 3.69, 3.79)
    }
    

    SCALA

    def getGasPrices(): (Double, Double, Double) = {
        return (3.59, 3.69, 3.79)
    }
    

    Scala 惯用法 IDIOMATIC SCALA

    def getGasPrices = (3.59, 3.69, 3.79)
    

    Variable Number Of Arguments 可变参数

    SWIFT

    func sumOf(numbers: Int...) -> Int {
        var sum = 0
        for number in numbers {
            sum += number
        }
        return sum
    }
    sumOf(42, 597, 12)
    

    SCALA

    def sumOf(numbers: Int*): Int = {
        var sum = 0
        for (number <- numbers) {
            sum += number
        }
        return sum
    }
    sumOf(42, 597, 12)
    

    Scala 惯用法 IDIOMATIC SCALA

    Array(42, 597, 12).sum
    

    Function Type 函数类型

    SWIFT

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

    SCALA

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

    Scala 惯用法 IDIOMATIC SCALA

    def makeIncrementer: Int => Int = 
        (number: Int) => 1 + number
    
    var increment = makeIncrementer
    increment(7)
    

    映射 Map

    SWIFT

    var numbers = [20, 19, 7, 12]
    numbers.map({ number in 3 * number })
    

    SCALA

    var numbers = Array(20, 19, 7, 12)
    numbers.map( number => 3 * number )
    

    排序 Sort

    SWIFT

    sort([1, 5, 3, 12, 2]) { $0 > $1 }
    

    SCALA

    Array(1, 5, 3, 12, 2).sortWith(_ > _)
    

    Named Arguments 命名参数

    SWIFT

    func area(#width: Int, #height: Int) -> Int {
        return width * height
    }
    
    area(width: 10, height: 10)
    

    SCALA

    def area(width: Int, height: Int): Int = {
        return width * height
    }
    
    area(width = 10, height = 10)
    

    Declaration 声明

    SWIFT

    class Shape {
        var numberOfSides = 0
        func simpleDescription() -> String {
            return "A shape with \(numberOfSides) sides."
        }
    }
    

    SCALA

    class Shape {
        var numberOfSides = 0
        def simpleDescription(): String = {
            return s"A shape with $numberOfSides sides."
        }
    }
    

    Scala 惯用法 IDIOMATIC SCALA

    class Shape (var numberOfSides: Int = 0) {
        def simpleDescription =
            s"A shape with $numberOfSides sides."
    }
    

    Usage 使用

    SWIFT

    var shape = Shape()
    shape.numberOfSides = 7
    var shapeDescription = shape.simpleDescription()
    

    SCALA

    var shape = new Shape()
    shape.numberOfSides = 7
    var shapeDescription = shape.simpleDescription()
    

    Subclass 子类

    SWIFT

    class NamedShape {
        var numberOfSides: Int = 0
        var name: String
    
        init(name: String) {
            self.name = name
        }
    
        func simpleDescription() -> String {
            return "A shape with \(numberOfSides) sides."
        }
    }
    
    class Square: NamedShape {
        var sideLength: Double
    
        init(sideLength: Double, name: String) {
            self.sideLength = sideLength
            super.init(name: name)
            numberOfSides = 4
        }
    
        func area() -> Double {
            return sideLength * sideLength
        }
    
        override func simpleDescription() -> String {
            return "A square with sides of length
                    \(sideLength)."
        }
    }
    
    let test = Square(sideLength: 5.2, name: "my test square")
    test.area()
    test.simpleDescription()
    

    Scala 惯用法 IDIOMATIC SCALA

    class NamedShape(var name: String,
                     var numberOfSides: Int = 0) {
        def simpleDescription =
            s"A shape with $numberOfSides sides."
    }
    
    class Square(var sideLength: Double, name: String)
        extends NamedShape(name, numberOfSides = 4) {
        def area = sideLength * sideLength
        override def simpleDescription =
            s"A square with sides of length $sideLength."
    }
    
    val test = new Square(5.2, "my test square")
    test.area
    test.simpleDescription
    

    类型检测 Checking Type

    SWIFT

    var movieCount = 0
    var songCount = 0
     
    for item in library {
        if item is Movie {
            ++movieCount
        } else if item is Song {
            ++songCount
        }
    }
    

    SCALA

    var movieCount = 0
    var songCount = 0
     
    for (item <- library) {
        if (item.isInstanceOf[Movie]) {
            movieCount += 1
        } else if (item.isInstanceOf[Song]) {
            songCount += 1
        }
    }
    

    Pattern Match 模式匹配

    SWIFT

    var movieCount = 0
    var songCount = 0
    
    for item in library {
      switch item {
        case let movie as Movie:
          ++movieCount
          println("Movie: '\(movie.name)', dir. \(movie.director)")
        case let song as Song:
          ++songCount
          println("Song: '\(song.title)'")
      }
    }
    

    SCALA

    var movieCount = 0
    var songCount = 0
    
    for (item <- library) {
      item match {
        case movie: Movie =>
          movieCount += 1
          println(s"Movie: '${movie.name}', dir. ${movie.director}")
        case song: Song =>
          songCount += 1
          println(s"Song: '${song.title}'")
      }
    }
    

    向下类型转换 Downcasting

    SWIFT

    for object in someObjects {
        let movie = object as Movie
        println("Movie: '\(movie.name)', dir. \(movie.director)")
    }
    

    SCALA

    for (obj <- someObjects) {
        val movie = obj.asInstanceOf[Movie]
        println(s"Movie: '${movie.name}', dir. ${movie.director}")
    }
    

    协议 Protocol

    SWIFT

    protocol Nameable {
        func name() -> String
    }
    
    func f<T: Nameable>(x: T) {
        println("Name is " + x.name())
    }
    

    SCALA

    trait Nameable {
        def name(): String
    }
    
    def f[T <: Nameable](x: T) = {
        println("Name is " + x.name())
    }
    

    类型扩展 Extensions

    SWIFT

    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 / 3.28084 }
    }
    let oneInch = 25.4.mm
    println("One inch is \(oneInch) meters")
    // prints "One inch is 0.0254 meters"
    let threeFeet = 3.ft
    println("Three feet is \(threeFeet) meters")
    // prints "Three feet is 0.914399970739201 meters"
    

    SCALA

    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 / 3.28084 }
        }
    }
    
    import Extensions.DoubleUnit
    
    val oneInch = 25.4.mm
    println(s"One inch is $oneInch meters")
    // prints "One inch is 0.0254 meters"
    val threeFeet = 3.ft
    println(s"Three feet is $threeFeet meters")
    // prints "Three feet is 0.914399970739201 meters"
    

    Scala惯用法 IDIOMATIC SCALA

    object Extensions {
        implicit class DoubleUnit(d: Double) {
            def km = d * 1000.0
            def m = d
            def cm = d / 100.0
            def mm = d / 1000.0
            def ft = d / 3.28084
        }
    }
    
    import Extensions.DoubleUnit
    
    val oneInch = 25.4.mm
    println(s"One inch is $oneInch meters")
    // prints "One inch is 0.0254 meters"
    val threeFeet = 3.ft
    println(s"Three feet is $threeFeet meters")
    // prints "Three feet is 0.914399970739201 meters"
    

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