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Kotlin/Swift语法对比

在公司flutter 开发已经近两年了,在flutter过程中经常需要编写插件,涉及到IOS端,想着一些简单逻辑的插件就自己写了,不需要劳烦ios同学了。之前虽然有玩过ios的demo,现在基本又忘了,自己观察了下,现在的高级语言语法已经愈发接近了。swift与传统oc差别巨大,却和我们安卓的kotlin语言甚是相似。

我们先来看看语法,这里主要拿来与kotlin对比

变量和常量

Swift

var myVariable = 42

let myConstant = 42
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Kotlin

var myVariable = 42

val myConstant = 42
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对比: 变量都是variable,常量kotlin是val,swift是let,let在js中主要是做局部变量,js中常量有const

类型声明

Swift

let explicitDouble: Double = 70
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Kotlin

val explicitDouble: Double = 70.0
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对比:类型的声明都是冒号

字符串插值

Swift

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

val apples = 3
val oranges = 5
val fruitSummary = "I have ${apples + oranges} " +
"pieces of fruit."
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对比:Swift使用 “\” 符号 Kotlin使用 “$” 符号

数组

Swift

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

val shoppingList = arrayOf("catfish", "water",
"tulips", "blue paint")
shoppingList[1] = "bottle of water"
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对比:swift是中括号,和dart一致,kotlin小括号

字典/map

Swift

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

val occupations = mutableMapOf(
"Malcolm" to "Captain",
"Kaylee" to "Mechanic"
)
occupations["Jayne"] = "Public Relations"
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对比:Swift使用 ":" 连接 key value 。Kotlin可用“to” 关键字 连接key value

函数定义

Swift

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

fun greet(name: String = "name", day: String= "sunday"): String {
return "Hello $name, today is $day."
}
greet("Bob", "Tuesday")
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对比: 1.kotlin方法定义fun , swift是func 2.Kotlin 返回值是冒号,swift是-> 。 3.swift用_代表忽略参数标签,不然都需要key-value形式一样去传参。 kotlin只有带有默认值的参数才需要带参数名 4.两者都有默认参数,高阶函数。swift返回值可以是元组。

Swift

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

class Shape {
    var numberOfSides = 0
    fun simpleDescription() =
        "A shape with $numberOfSides sides."
}
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对象实例化

Swift

var shape = Shape()
shape.numberOfSides = 7
var shapeDescription = shape.simpleDescription()
Kotlin
var shape = Shape()
shape.numberOfSides = 7
var shapeDescription = shape.simpleDescription()
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子类继承

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()
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Kotlin Kotlin类继承,需在父类用open关键字显式声明

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()
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OC/swift的协议 对标java和kotlin的接口

Swift Swift使用 protocol 关键字

protocol Nameable {
    func name() -> String
}

func f<T: Nameable>(x: T) {
    print("Name is " + x.name())
}
Kotlin
Kotlin使用 interface 关键字

interface Nameable {
    fun name(): String
}

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

Swift Swift需使用extension关键字

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")
// 输出 "One inch is 0.0254 meters"
let threeFeet = 3.ft
print("Three feet is \(threeFeet) meters")
// 输出 "Three feet is 0.914399970739201 meters"
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Kotlin Kotlin则直接使用“.”符号

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")
// 输出 "One inch is 0.0254 meters"
val threeFeet = 3.0.ft
println("Three feet is $threeFeet meters")
// 输出 "Three feet is 0.914399970739201 meters"
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这里主要列出了一些日常常用的一些语法,可见kotlin和swfit差别并不大,基本上看一下差别就是可以直接上手的。当然还有很多东西是需要深入了解的,线程相关的kotlin协程和swift的GCD等等。
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