Kotlin 就像Swift ？看看 Kotlin 与 Swift 的简单对比

Posted 2021-04-01 安卓开发

tags:

篇首语：本文由小常识网(cha138.com)小编为大家整理，主要介绍了Kotlin 就像Swift ？看看 Kotlin 与 Swift 的简单对比相关的知识，希望对你有一定的参考价值。

文章转载自开源中国社区

链接：www.oschina.net/news/85013/swift-is-like-kotlin（点击尾部阅读原文前往）

原文：http://nilhcem.com/swift-is-like-kotlin/

一位国外的程序员认为 Swift 的语法与 Kotlin 相似，并整理了一些 Swift 和 Kotlin 的对比，下面是一些例子，大家不妨也看看。

BASICS

Hello World

Swift

print("Hello, world!")

Kotlin

println("Hello, world!")

变量和常量

Swift

var myVariable = 42

myVariable = 50

let myConstant = 42

Kotlin

var myVariable = 42

myVariable = 50

val myConstant = 42

显式类型

Swift

let explicitDouble: Double = 70

Kotlin

val explicitDouble: Double = 70.0

强制类型转换

Swift

let label = "The width is "

let width = 94

let widthLabel = label + String(width)

Kotlin

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."

Kotlin

val apples = 3

val oranges = 5

val fruitSummary = "I have ${apples + oranges} " +

"pieces of fruit."

范围操作符

Swift

let names = ["Anna", "Alex", "Brian", "Jack"]

let count = names.count

for i in 0..

Kotlin

val names = arrayOf("Anna", "Alex", "Brian", "Jack")

val count = names.count()

for (i in 0..count - 1) {

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

包罗广泛的范围操作符（Inclusive Range Operator）

Swift

for index in 1...5 {

print("(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

Kotlin

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

BASICS

数组

Swift

var shoppingList = ["catfish", "water",

"tulips", "blue paint"]

shoppingList[1] = "bottle of water"

Kotlin

val shoppingList = arrayOf("catfish", "water",

"tulips", "blue paint")

shoppingList[1] = "bottle of water"

映射

Swift

var occupations = [

"Malcolm": "Captain",

"Kaylee": "Mechanic",

]

occupations["Jayne"] = "Public Relations"

Kotlin

val occupations = mutableMapOf(

"Malcolm" to "Captain",

"Kaylee" to "Mechanic"

)

occupations["Jayne"] = "Public Relations"

空集合

Swift

let emptyArray = [String]()

let emptyDictionary = [String: Float]()

Kotlin

val emptyArray = arrayOf()

val emptyMap = mapOf()

FUNCTIONS

函数

Swift

func greet(_ name: String,_ day: String) -> String {

return "Hello (name), today is (day)."

}

greet("Bob", "Tuesday")

Kotlin

fun greet(name: String, day: String): String {

return "Hello $name, today is $day."

}

greet("Bob", "Tuesday")

元组返回

Swift

func getGasPrices() -> (Double, Double, Double) {

return (3.59, 3.69, 3.79)

}

Kotlin

data class GasPrices(val a: Double, val b: Double,

val c: Double)

fun getGasPrices() = GasPrices(3.59, 3.69, 3.79)

参数的变量数目（Variable Number Of Arguments）

Swift

func sumOf(_ numbers: Int...) -> Int {

    var sum = 0

    for number in numbers {

        sum += number

    }

    return sum

}

sumOf(42, 597, 12)

Kotlin

fun sumOf(vararg numbers: Int): Int {

    var sum = 0

    for (number in numbers) {

        sum += number

    }

    return sum

}

sumOf(42, 597, 12)

// sumOf() can also be written in a shorter way:

fun sumOf(vararg numbers: Int) = numbers.sum()

函数类型

Swift

func makeIncrementer() -> (Int -> Int) {

    func addOne(number: Int) -> Int {

        return 1 + number

    }

    return addOne

}

let increment = makeIncrementer()

increment(7)

Kotlin

fun makeIncrementer(): (Int) -> Int {

    val addOne = fun(number: Int): Int {

        return 1 + number

    }

    return addOne

}

val increment = makeIncrementer()

increment(7)

// makeIncrementer can also be written in a shorter way:

fun makeIncrementer() = fun(number: Int) = 1 + number

映射

Swift

let numbers = [20, 19, 7, 12]

numbers.map { 3 * $0 }

Kotlin

val numbers = listOf(20, 19, 7, 12)

numbers.map { 3 * it }

排序

Swift

var mutableArray = [1, 5, 3, 12, 2]

mutableArray.sort()

Kotlin

listOf(1, 5, 3, 12, 2).sorted()

命名参数

Swift

func area(width: Int, height: Int) -> Int {

return width * height

}

area(width: 2, height: 3)

Kotlin

fun area(width: Int, height: Int) = width * height

area(width = 2, height = 3)

// This is also possible with named arguments

area(2, height = 2)

area(height = 3, width = 2)

CLASSES

声明

Swift

class Shape {

    var numberOfSides = 0

    func simpleDescription() -> String {

        return "A shape with (numberOfSides) sides."

    }

}

Kotlin

class Shape {

    var numberOfSides = 0

    fun simpleDescription() =

        "A shape with $numberOfSides sides."

}

用法

Swift

var shape = Shape()

shape.numberOfSides = 7

var shapeDescription = shape.simpleDescription()

Kotlin

var shape = Shape()

shape.numberOfSides = 7

var shapeDescription = shape.simpleDescription()

子类

Swift

class NamedShape {

    var numberOfSides: Int = 0

    let 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)

        self.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: "square")

test.area()

test.simpleDescription()

Kotlin

open class NamedShape(val name: String) {

    var numberOfSides = 0

    open fun simpleDescription() =

        "A shape with $numberOfSides sides."

}

class Square(var sideLength: BigDecimal, name: String) :

        NamedShape(name) {

    init {

        numberOfSides = 4

    }

    fun area() = sideLength.pow(2)

    override fun simpleDescription() =

        "A square with sides of length $sideLength."

}

val test = Square(BigDecimal("5.2"), "square")

test.area()

test.simpleDescription()

类型检查

Swift

var movieCount = 0

var songCount = 0

for item in library {

    if item is Movie {

        movieCount += 1

    } else if item is Song {

        songCount += 1

    }

}

Kotlin

var movieCount = 0

var songCount = 0

for (item in library) {

    if (item is Movie) {

        ++movieCount

    } else if (item is Song) {

        ++songCount

    }

}

模式匹配

Swift

let nb = 42

switch nb {

    case 0...7, 8, 9: print("single digit")

    case 10: print("double digits")

    case 11...99: print("double digits")

    case 100...999: print("triple digits")

    default: print("four or more digits")

}

Kotlin

val nb = 42

when (nb) {

    in 0..7, 8, 9 -> println("single digit")

    10 -> println("double digits")

    in 11..99 -> println("double digits")

    in 100..999 -> println("triple digits")

    else -> println("four or more digits")

}

类型向下转换

Swift

for current in someObjects {

    if let movie = current as? Movie {

        print("Movie: '(movie.name)', " +

            "dir. (movie.director)")

    }

}

Kotlin

for (current in someObjects) {

    if (current is Movie) {

        println("Movie: '${current.name}', " +

    "dir. ${current.director}")

    }

}

协议

Swift

protocol Nameable {

func name() -> String

}

func f(x: T) {

print("Name is " + x.name())

}

Kotlin

interface Nameable {

fun name(): String

}

fun f(x: T) {

println("Name is " + x.name())

}

扩展

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

print("One inch is (oneInch) meters")

// prints "One inch is 0.0254 meters"

let threeFeet = 3.ft

print("Three feet is (threeFeet) meters")

// prints "Three feet is 0.914399970739201 meters"

Kotlin

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 / 3.28084

val oneInch = 25.4.mm

println("One inch is $oneInch meters")

// prints "One inch is 0.0254 meters"

val threeFeet = 3.0.ft

println("Three feet is $threeFeet meters")

// prints "Three feet is 0.914399970739201 meters"

●本文编号199，以后想阅读这篇文章直接输入199即可。

●输入m获取文章目录