常量与变量
let maximumNumberOfLoginAttempts = 10
var currentLoginAttempt 0
x 0.0,y z 0.0
welcomeMessage: String
welcomeMessage = "Hello"
π 3.14159
let 你好 = "你好世界"
let □□"dogcow"
welcomeMessage: String
welcomeMessage = "Hello"
π 3.14159
let 你好 = "你好世界"
let □□"dogcow"
friendlyWelcome "Hello!"
"Bonjour!"
// friendlyWelcome is now "Bonjour!"
"Bonjour!"
// friendlyWelcome is now "Bonjour!"
languageName "Swift"
"Swift++"
// this is a compile-time error - languageName cannot be changed
"Swift++"
// this is a compile-time error - languageName cannot be changed
println(friendlyWelcome)
// prints "Bonjour!"
("This is a string"// prints "This is a string"
// prints "Bonjour!"
("This is a string"// prints "This is a string"
"The current value of friendlyWelcome is \()"// prints "The current value of friendlyWelcome is Bonjour!"
注释
// this is a comment
/* this is also a comment,
but written over multiple lines */
/* this is the start of the first multiline comment
/* this is the second,nested multiline comment */
this is the end of the first multiline comment */
/* this is also a comment,
but written over multiple lines */
/* this is the start of the first multiline comment
/* this is the second,nested multiline comment */
this is the end of the first multiline comment */
分号
let
cat
=
"□"
;
println
(
cat
)
// prints "□"
// prints "□"
整型数
let
minValue
=
UInt8
.
min
// minValue is equal to 0,and is of type UInt8
let maxValue = UInt8 . max // maxValue is equal to 255,and is of type UInt8
On a 32-bit platform,Int is the same size as Int32.
On a 64-bit platform,128)"> Int is the same size as Int64.
On a 32-bit platform,128)"> UInt UInt32 UInt64.
// meaningOfLife is inferred to be of type Int
pi // pi is inferred to be of type Double
anotherPi 3 + 0.14159
// anotherPi is also inferred to be of type Double
let maxValue = UInt8 . max // maxValue is equal to 255,and is of type UInt8
On a 32-bit platform,Int is the same size as Int32.
On a 64-bit platform,128)"> Int is the same size as Int64.
On a 32-bit platform,128)"> UInt UInt32 UInt64.
类型安全与类型推理
meaningOfLife 42// meaningOfLife is inferred to be of type Int
pi // pi is inferred to be of type Double
anotherPi 3 + 0.14159
// anotherPi is also inferred to be of type Double
数字字面常量
decimalInteger 17
binaryInteger 0b10001 // 17 in binary notation
octalInteger 0o21 // 17 in octal notation
hexadecimalInteger 0x11 // 17 in hexadecimal notation
1.25e2 means 1.25 × 102,or 125.0.
1.25e-2 means 1.25 × 10-2,128)"> 0.0125.
0xFp2 means 15 × 22,128)">60.00xFp-2 means 15 × 2-2,128)"> 3.75.
decimalDouble 12.1875
exponentDouble 1.21875e1
hexadecimalDouble 0xC.3p0
paddedDouble 000123.456
oneMillion 1_000_000
justOverOneMillion 1_000_000.000_000_1
binaryInteger 0b10001 // 17 in binary notation
octalInteger 0o21 // 17 in octal notation
hexadecimalInteger 0x11 // 17 in hexadecimal notation
1.25e2 means 1.25 × 102,or 125.0.
1.25e-2 means 1.25 × 10-2,128)"> 0.0125.
0xFp2 means 15 × 22,128)">60.00xFp-2 means 15 × 2-2,128)"> 3.75.
decimalDouble 12.1875
exponentDouble 1.21875e1
hexadecimalDouble 0xC.3p0
paddedDouble 000123.456
oneMillion 1_000_000
justOverOneMillion 1_000_000.000_000_1
数字类型转换
cannotBeNegativeUInt8 = -1
// UInt8 cannot store negative numbers,and so this will report an error
tooBigInt8 = Int8.max + 1
// Int8 cannot store a number larger than its maximum value,18)">// and so this will also report an error
twoThousandUInt16 2_000
onetwoThousandAndOne twoThousand + UInt16)
three 3
pointOneFourOneFiveNine Doublethree) + pointOneFourOneFiveNine
// pi equals 3.14159,and is inferred to be of type Double
integerPi Intpi// integerPi equals 3,and is inferred to be of type Int
maxAmplitudeFound AudioSamplemin
// maxAmplitudeFound is now 0
// UInt8 cannot store negative numbers,and so this will report an error
tooBigInt8 = Int8.max + 1
// Int8 cannot store a number larger than its maximum value,18)">// and so this will also report an error
twoThousandUInt16 2_000
onetwoThousandAndOne twoThousand + UInt16)
three 3
pointOneFourOneFiveNine Doublethree) + pointOneFourOneFiveNine
// pi equals 3.14159,and is inferred to be of type Double
integerPi Intpi// integerPi equals 3,and is inferred to be of type Int
类型别名
typealias AudioSample = UInt16maxAmplitudeFound AudioSamplemin
// maxAmplitudeFound is now 0
布尔型
orangesAreOrange true
turnipsAreDelicIoUs false
if {
println"Mmm,tasty turnips!"} else "Eww,turnips are horrible."}
// prints "Eww,turnips are horrible."
i == 1 // this example will compile successfully
}
"The status code is \(// prints "The status code is 404"
"The status message is // prints "The status message is Not Found"
justTheStatusCode_// prints "The status code is 404"
http404Error.01// prints "The status message is Not Found"
http200Status = (: 200description: "OK")
http200Status// prints "The status code is 200"
// prints "The status message is OK"
turnipsAreDelicIoUs false
if {
println"Mmm,tasty turnips!"} else "Eww,turnips are horrible."}
// prints "Eww,turnips are horrible."
i == 1 // this example will compile successfully
}
元组
let statusCodestatusMessage) = http404Error"The status code is \(// prints "The status code is 404"
"The status message is // prints "The status message is Not Found"
justTheStatusCode_// prints "The status code is 404"
http404Error.01// prints "The status message is Not Found"
http200Status = (: 200description: "OK")
http200Status// prints "The status code is 200"
// prints "The status message is OK"
可选类型
possibleNumber "123"
convertedNumber possibleNumbertoInt()
// convertedNumber is inferred to be of type "Int?",or "optional Int"
) has an integer value of convertedNumber!)could not be converted to an integer"// prints "123 has an integer value of 123"
if let actualNumber () {
actualNumber// prints "123 has an integer value of 123"
convertedNumber possibleNumbertoInt()
// convertedNumber is inferred to be of type "Int?",or "optional Int"
) has an integer value of convertedNumber!)could not be converted to an integer"// prints "123 has an integer value of 123"
if let actualNumber () {
actualNumber// prints "123 has an integer value of 123"
空值(nil)
serverResponseCodeInt? = 404
// serverResponseCode contains an actual Int value of 404
serverResponseCode = nil
// serverResponseCode now contains no value
surveyAnswerString?
// surveyAnswer is automatically set to nil
!) // requires an exclamation mark to access its value
// prints "An optional string."
assumedString String! = "An implicitly unwrapped optional string."
assumedString) // no exclamation mark is needed to access its value
// prints "An implicitly unwrapped optional string."
assumedString // prints "An implicitly unwrapped optional string."
// serverResponseCode contains an actual Int value of 404
serverResponseCode = nil
// serverResponseCode now contains no value
surveyAnswerString?
// surveyAnswer is automatically set to nil
隐式可选类型
possibleString? = "An optional string."!) // requires an exclamation mark to access its value
// prints "An optional string."
assumedString String! = "An implicitly unwrapped optional string."
assumedString) // no exclamation mark is needed to access its value
// prints "An implicitly unwrapped optional string."
assumedString // prints "An implicitly unwrapped optional string."
断言
age assert>= 0 "A person's age cannot be less than zero"// this causes the assertion to trigger,because age is not >= 0
