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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
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?+?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?${apples?+?oranges}?"?"pieces?of?fruit."
范围操作符
Swift
let?names?=?["Anna",?"Alex""Brian""Jack"]
let?count?=?names.count
for?i?in?0..
Kotlin
val?names?=?arrayOf()
val?count?.count()
for?(i?in?0..count?-?1)?{
????println("Person?${i?+?1}?is?called?${names[i]}")
}
//?Person?1?is?called?Anna
//?Person?2?is?called?Alex
//?Person?3?is?called?Brian
//?Person?4?is?called?Jack
包罗广泛的范围操作符（Inclusive Range Operator）
Swift
for?index?in?1...5?{
????print"(index)?times?5?is?(index?*?5)"//?1?times?5?is?5
//?2?times?5?is?10
//?3?times?5?is?15
//?4?times?5?is?20
//?5?times?5?is?25
Kotlin
for?(index?in?1..5)?"$index?times?5?is?${index?*?5}"//?5?times?5?is?25
数组
Swift
var?shoppingList?"catfish""water"????"tulips""blue?paint"]
shoppingList[]?"bottle?of?water"
Kotlin
val?shoppingList?)
"bottle?of?water"
映射
Swift
var?occupations?[
????"Malcolm":?"Captain""Kaylee""Mechanic"]
occupations["Jayne""Public?Relations"
Kotlin
val?occupations?=?mutableMapOf(
????"Malcolm"?to?"Kaylee"?to?"Mechanic"
)
"Public?Relations"
空集合
Swift
let?emptyArray?[String]()
let?emptyDictionary?=?[String:?Float]()
Kotlin
val?emptyArray?()
val?emptyMap?=?mapOf()
FUNCTIONS
函数
Swift
func?greet(_?name:?_?day)?->?String?{
????return?"Hello?(name),?today?is?(day)."
}
greet"Bob""Tuesday")
Kotlin
fun?greet()"Hello?$name,?today?is?$day."
)
元组返回
Swift
func?getGasPrices()?->?(Double{
????return?(3.593.693.79}
Kotlin
data?class?GasPrices(val?aval?b?????val?cDouble)
fun?getGasPrices()?=?GasPrices参数的变量数目（Variable Number Of Arguments）
Swift
func?sumOfnumbersInt...)?Int?{
????var?sum?0
????for?number?in?numbers?{
????????sum?+=?number
????}
????return?sum
}
sumOf4259712)
Kotlin
fun?sumOf(vararg?0
????for?(number?in?numbers)
?
//?sumOf()?can?also?be?written?in?a?shorter?way:
fun?sumOf(vararg?numbersInt)?.sum函数类型
Swift
func?makeIncrementerInt?{
????func?addOnenumber->?Int?{
????????return?1?+?number
????}
????return?addOne
}
let?increment?=?makeIncrementer()
increment7)
Kotlin
fun?makeIncrementer():?{
????val?addOne?=?fun)}
val?increment?//?makeIncrementer?can?also?be?written?in?a?shorter?way:
fun?makeIncrementernumber
映射
Swift
let?numbers?[2019712.map?{?3?*?$0?}
Kotlin
val?numbers?=?listOf(*?it?}
排序
Swift
var?mutableArray?1532mutableArray.sort()
Kotlin
listOf(1,?5,?3,?12,?2).sorted()
命名参数
Swift
func?areawidthheight{
????return?width?*?height
}
areawidth:?2height3)
Kotlin
fun?area=?width?*?height
area(width?height?//?This?is?also?possible?with?named?arguments
area)
area(height?width?CLASSES
声明
Swift
class?Shape?var?numberOfSides?0
????func?simpleDescriptionString?{
????????return?"A?shape?with?(numberOfSides)?sides."
????}
}
Kotlin
0
????fun?simpleDescription=
????????"A?shape?with?$numberOfSides?sides."
}
用法
Swift
var?shape?=?Shape()
shape.numberOfSides?7
var?shapeDescription?.simpleDescription()
Kotlin
子类
Swift
class?NamedShape?var?numberOfSidesInt?0
????let?nameString
?
????init{
????????self.name?=?name
????}
?
????func?simpleDescription}
?
class?Square:?NamedShape?sideLengthDouble
?
????init.sideLength?=?sideLength
????????super.init:?name)
????????self4
????}
?
????func?areaDouble?{
????????return?sideLength?*?sideLength
????}
?
????override?func?simpleDescription"A?square?with?sides?of?length?"?+
???????sideLength?+?"."
????}
?
let?test?=?Square5.2"square"test.area()
Kotlin
open?class?NamedShape0
?
????open?fun?simpleDescriptionclass?Square(BigDecimal:
????????NamedShape{
????init?{
????????numberOfSides?}
?
????fun?areasideLength.pow)
?
????override?fun?simpleDescription"A?square?with?sides?of?length?$sideLength."
}
?
val?test?(BigDecimal"5.2"),66);">类型检查
Swift
var?movieCount?0
var?songCount?0
?
for?item?in?library?{
????if?item?is?Movie?{
????????movieCount?+=?1
????}?else?if?item?is?Song?{
????????songCount?0
?
for?(item?in?library{
????if?(item?is?Movie{
????????++movieCount
????}?else?if?Song++songCount
????模式匹配
Swift
let?nb?42
switch?nb?{
????case?0...789:?print"single?digit")
????case?10"double?digits"11...99100...999"triple?digits")
????default"four?or?more?digits"}
Kotlin
val?nb?42
when?nb{
????in?0..79?->?println)
????10?)
????in?11..99?100..999?)
????else?类型向下转换
Swift
for?current?in?someObjects?{
????if?let?movie?=?current?as??Movie?{
????????print"Movie:?'(movie.name)',?"?+
????????????"dir.?(movie.director)")
????}
Kotlin
for?(current?in?someObjects(current?is?{
????????println"Movie:?'${current.name}',224) !important;"> ????"dir.?${current.director}"协议
Swift
protocol?Nameable?{
????func?nameString
}
?
func?fxT"Name?is?"?x.name())
interface?Nameable?{
????fun?name()}
?
fun?f扩展
Swift
extension?Double?km{?return?self?*?1_000.0?}
????m{?return?self?cm/?100.0?mmft3.28084?}
let?oneInch?25.4.mm
print"One?inch?is?(oneInch)?meters")
//?prints?"One?inch?is?0.0254?meters"
let?threeFeet?3.ft
print"Three?feet?is?(threeFeet)?meters"//?prints?"Three?feet?is?0.914399970739201?meters"
Kotlin
val?.kmDouble?get=?this?*?1000
val?.Double?get=?this
val?=?this?100
val?3.28084
?
val?oneInch?25.4.mm
println"One?inch?is?$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"
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