簡介:
Swift發(fā)布后提供了很多高效的標(biāo)準(zhǔn)庫函數(shù),其實(shí)早在 Swift 正式發(fā)布之前，iOS / Cocoa 開發(fā)者都可以使用諸如 ObjectiveSugar 或者 ReactiveCocoa 第三方庫，實(shí)現(xiàn)類似 map、flatMap 或 filter 等函數(shù)式編程的構(gòu)建。
并且通過使用函數(shù)式編程能夠更好地表達(dá)你的意圖，減少代碼的行數(shù)，以及使用鏈?zhǔn)浇Y(jié)構(gòu)構(gòu)建復(fù)雜的邏輯，更顯清爽。

接下來,介紹一下常用的一些標(biāo)準(zhǔn)庫函數(shù):

1.在文檔中提到的庫函數(shù)(The Swift Programming Language)

//斷言，參數(shù)如果為true則繼續(xù)，否則拋出異常
assert(true)

//swift 1.0 計(jì)算序列的元素個(gè)數(shù)
let str = "sk87v5"
countElements("str") == 6

//swift2.0后計(jì)算字符串長度
print(str.characters.count)//6

//swift2.0后計(jì)算數(shù)組元素
let arr = ["sk", "wyj", "jj"]
print(arr.count)//3

//返回一個(gè)新的序列，其中每個(gè)元素是一個(gè)元組，第一個(gè)值為原來元素所在的位置index，第二個(gè)為原來序列中的元素
let array = ["N", "B","A"]
for (i, j) in array.enumerate() {
    print("\(i):\(j)")
}
打印結(jié)果:
//0:N
//1:B
//2:A

//返回所有參數(shù)中的最小值
min(9, 2, 4) == 2

//打印
print("Hello")

//Swift1.0 使用的打印 （帶換行)
// println mentioned on page 4
println("World")

//排序
// sort mentioned on page 14
let array = ["N", "B","A"]
for i in array.sort() {
    print(i) // A B N
}

2.文檔未提的實(shí)用函數(shù)

• Swift 1.0
• map(sequence, transformClosure)：對(duì)數(shù)組中每個(gè)元素都執(zhí)行閉包，并將所有閉包的結(jié)果合成一個(gè)新數(shù)組并返回。
• Swift 2.0
• map(transform: (Int) throws -> T):對(duì)數(shù)組中每個(gè)元素都執(zhí)行閉包中的操作，并將所有閉包的結(jié)果合成一個(gè)新序列數(shù)組并返回。

//swift 2.0
let array = [1, 10, 22, 40, 88, 90, 99]
//1.常規(guī)用法
let newArr = array.map { (a : Int) -> Int in
    return a + 10
}
print(newArr)

//2.簡化用法
let newArr = array.map({$0 + 10})
print(newArr)
//打印結(jié)果:
[11, 20, 32, 50, 98, 100, 109]

• (Swift 1.0)
• filter(sequence, includeElementClosure)：
• (Swift 2.0)
• filter(includeElement: (Int) throws -> Bool)
  對(duì)序列數(shù)組中每個(gè)元素都執(zhí)行includeElement閉包，并將所有閉包結(jié)果為true的元素合成一個(gè)新數(shù)組并返回。

//swift 2.0
let array = [1, 10, 22, 40, 88, 90, 99]
//1.常規(guī)用法
let newArr = array.filter { (a : Int) -> Bool in
    return a % 10 == 0
}
print(newArr)//[10, 40, 90]\n

//2.簡化用法
let newArr = array.filter({$0 % 10 == 0})
print(newArr)//[10, 40, 90]\n

• Swift 1.0
• reduce(sequence, initial, combineClosure)：給定一個(gè)數(shù)組sequence，以及一個(gè)初始值initial，然后將initial和數(shù)組里的第1個(gè)元素作為參數(shù)傳入combineClosure閉包中進(jìn)行運(yùn)算，得到的結(jié)果保存到initial；然后再將initial和第2個(gè)元素傳入combineClosure閉包中計(jì)算，結(jié)果保存到initial；重復(fù)計(jì)算直到所有sequence中的元素都計(jì)算完畢，并返回最終的initial值。
• Swift 2.0
• reduce(initial: T, combine: (T, String) throws -> T)

//1.傳統(tǒng)求和
let arrNum = [1, 2, 3, 4 ,5]
var sum = 0
for num in arrNum {
    sum = sum + num
}
print(sum) //15

//2.傳統(tǒng)求積
var a = 1
for num in arrNum {
    a = a * num
}
print(a)//120

//2.reduce求和,求積:
let arrNum = [1, 2, 3, 4, 5]
//簡化一:
let sum = arrNum.reduce(0, combine: {$0 + $1})
let a = arrNum.reduce(1, combine: {$0 * $1})

//簡化二:
//初始值 initial 為 0，每次遍歷數(shù)組元素，執(zhí)行 + 操作
let sum = arrNum.reduce(0, combine: +)
//初始值 initial 為 1，每次遍歷數(shù)組元素，執(zhí)行 * 操作
let a = arrNum.reduce(1, combine: *)

print(sum)
print(a)

let arr = ["sk", "wyj", "jj", "dyf", "zjz"]
let arrNew = arr.reduce("87v5", combine: + )
print(arrNew)

• abs(signedNumber)：返回?cái)?shù)字的絕對(duì)值

abs(-1) == 1 //true
abs(-42) == 42 //true
abs(42) == 42 //true

• contains(sequence, element)：
• 如果某個(gè)序列sequence（比如說一個(gè)數(shù)組）包含指定的元素element，則返回true，否則返回false。

let arr = ["sk", "wyj", "jj", "dyf", "zjz"]
arr.contains("sk")// true
arr.contains("87v5")// false

• dropFirst(sequence)：
• 返回一個(gè)去掉了首個(gè)元素的、新的序列（比如一個(gè)新數(shù)組）。

let array = ["xmg", "sk", "why"]
var arrayNew = array.dropFirst() //["sk", "why"]
//去掉前2個(gè)元素
var arrayNewTwo = array.dropFirst(2) //["why"]
//注:elementsEqual() iOS9.0后可用
arrayNew.elementsEqual(array) //false

• dropLast(sequence)：返回一個(gè)去掉了最后一個(gè)元素的、新的序列（比如一個(gè)新數(shù)組）。

let array = ["xmg", "sk", "why"]
var arrayNew = array.dropLast() //["xmg", "sk"]
//去掉后2個(gè)元素
var arrayNewTwo = array.dropLast(2) //["xmg"]
arrayNew.elementsEqual(["xmg", "sk"])  //true

• dump(object)：打印出某個(gè)對(duì)象object的所有信息

let array = ["xmg", "sk", "why"]
dump(array) //["xmg", "sk", "why"]
// Prints:
//3 elements
//- [0]: xmg
//- [1]: sk
//- [2]: why

//注:dump和print的區(qū)別:dump打印的是內(nèi)容,print打印的是內(nèi)容+ 換行符的字符串
print(array)//"["xmg", "sk", "why"]\n"

• elementsEqual()：判斷兩個(gè)序列是否相等

let array = ["xmg", "sk", "why"]
array.elementsEqual(["sk"]) //false

let arrayOne = array.dropLast()
let arrayTwo = ["xmg", "sk"]
arrayOne.elementsEqual(arrayTwo) //true

• (Swift1.0)
• find(sequence, element)：返回序列sequence中某元素element的位置index。如果序列中不存在此元素，則返回nil。
• (Swift2.0)
• arr.indexOf(element: String):返回?cái)?shù)組中某元素element的位置index。如果數(shù)組中不存在此元素，則返回nil

//find(sequence, element)
let arr = ["sk", "wyj", "jj"]
find(arr, "sk") == 0
find(arr, "dyf") == nil
find([29, 85, 42, 96, 75], 42) == 2

//indexOf(element: String)
let arr = ["sk", "wyj", "jj"]
let index = arr.indexOf("sk") //0
let index2 = arr.indexOf("dyf")//nil

• (Swift 1.0)
• indices(sequence)：返回序列sequence中所有元素的位置（indices是index的復(fù)數(shù)）
• (Swift 2.0)
• 改為屬性indices,返回Range類型

//swift1.0
equal(indices([29, 85, 42]), [0, 1, 2])
for i in indices([29, 85, 42]) {
    // 0, 1, 2
    print(i)
}

//swift2.0
let arr = ["sk", "wyj", "jj"]
let a = arr.indices
print(a) //0..<3

• (Swift1.0)
• join(separator, sequence)：將序列sequence通過分隔符separator連成一個(gè)字符串，并返回此字符串。
• (Swift2.0)
• joinWithSeparator(separator: String)

//swift1.0
join(":", ["A", "B", "C"]) == "A:B:C"
let arr = ["sk", "wyj", "jj"]
join("/", arr) == "sk/wyj/jj"

//swift2.0
let arr = ["sk", "wyj", "jj"]
let joinArr = arr.joinWithSeparator("/")
print(joinArr)
打印結(jié)果:
sk/wyj/jj

• max(comparable1, comparable2, etc.)：返回參數(shù)中的最大值。

max(0, 1) == 1
max(8, 2, 3) == 8

• maxElement(sequence)：返回序列sequence中的最大值。

//swift 1.0
let array = [1, 10, 22, 40, 88, 90, 99]
maxElement(array) //99

//swift 2.0
let array = [1, 10, 22, 40, 88, 90, 99]
array.maxElement() //99

• minElements(sequence)：返回序列sequence中的最小值。

//swift 1.0
let array = [1, 10, 22, 40, 88, 90, 99]
minElement(array) //1

//swift 2.0
let array = [1, 10, 22, 40, 88, 90, 99]
array.minElement() //1

• reverse(sequence)：返回逆序的序列sequence。

let array = [1, 10, 22, 40, 88, 90, 99]
for i in array.reverse() {
    print(i)
}

• Swift 1.0
• startsWith(sequence1, sequence2)：如果序列sequence1中開頭的元素跟序列sequence2中的所有元素都相等，則返回true，否則返回false。
• Swift 2.0
• startsWith(other: SequenceType)

//swift 1.0
startsWith(1..20, 1..5) == true

let arr1 = ["sk", "wyj", "jj"]
let arr2 = ["sk"]
startsWith(arr1, arr2) == true

//swift 2.0
let range1 = 1..<20
let range2 = 1..<5
if range1.startsWith(range2) {
    print("range2所有元素和range1開頭元素相等")
}else {
    print("不相等")
}

let arr1 = ["sk", "wyj", "jj"]
let arr2 = ["sk"]
if arr1.startsWith(arr2) {
    print("arr2所有元素和arr1開頭所有元素相等")
}else {
    print("不相等")
}

附:Swift1.0 中74個(gè)內(nèi)置函數(shù)：

abs(...)
advance(...)
alignof(...)
alignofValue(...)
assert(...)
bridgeFromObjectiveC(...)
bridgeFromObjectiveCUnconditional(...)
bridgeToObjectiveC(...)
bridgeToObjectiveCUnconditional(...)
c_malloc_size(...)
c_memcpy(...)
c_putchar(...)
contains(...)
count(...)
countElements(...)
countLeadingZeros(...)
debugPrint(...)
debugPrintln(...)
distance(...)
dropFirst(...)
dropLast(...)
dump(...)
encodeBitsAsWords(...)
enumerate(...)
equal(...)
filter(...)
find(...)
getBridgedObjectiveCType(...)
getVaList(...)
indices(...)
insertionSort(...)
isBridgedToObjectiveC(...)
isBridgedVerbatimToObjectiveC(...)
isUniquelyReferenced(...)
join(...)
lexicographicalCompare(...)
map(...)
max(...)
maxElement(...)
min(...)
minElement(...)
numericCast(...)
partition(...)
posix_read(...)
posix_write(...)
print(...)
println(...)
quickSort(...)
reduce(...)
reflect(...)
reinterpretCast(...)
reverse(...)
roundUpToAlignment(...)
sizeof(...)
sizeofValue(...)
sort(...)
split(...)
startsWith(...)
strideof(...)
strideofValue(...)
swap(...)
swift_MagicMirrorData_summaryImpl(...)
swift_bufferAllocate(...)
swift_keepAlive(...)
toString(...)
transcode(...)
underestimateCount(...)
unsafeReflect(...)
withExtendedLifetime(...)
withObjectAtPlusZero(...)
withUnsafePointer(...)
withUnsafePointerToObject(...)
withUnsafePointers(...)
withVaList(...)

codeStraight原創(chuàng)文章,如有錯(cuò)誤,歡迎指正!
http://www.itdecent.cn/p/2c7407c76ad8