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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
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
