Swift包含了74個(gè)內(nèi)置函數(shù)，這里針對(duì)幾個(gè)我常用的內(nèi)置函數(shù)做一些總結(jié)。(內(nèi)置函數(shù)是指無(wú)需引入任何Module就可以直接使用的函數(shù))
1.斷言 assert，如果參數(shù)為 ture，則繼續(xù)，否則拋出異常
> 示例
let num = 3
//第一個(gè)參數(shù)為判斷條件，第二各參數(shù)為條件不滿足時(shí)的打印信息
assert(num > 3,"num 不大于 3")
//如果斷言被觸發(fā)(num <= 3)，將會(huì)強(qiáng)制結(jié)束程序，并打印相關(guān)信息
assertion failed: num 不大于 3
斷言可以引發(fā)程序終止，主要用于調(diào)試階段。比如下面的情況：
* 數(shù)組索引越界問(wèn)題
* 向函數(shù)傳值，無(wú)效值引發(fā)函數(shù)不能完成相應(yīng)任務(wù)
* Optional類型數(shù)據(jù)為nil值，引發(fā)的程序crash
2.獲取序列的元素個(gè)數(shù) characters.count (countElements)
> 示例
let str = "Hello world!"
//打印元素個(gè)數(shù)
print("count == \(str.characters.count)")
//打印結(jié)果
count == 3
3.將原有序列轉(zhuǎn)換成以元組作為元素的序列輸出 enumerated()
> 示例
let arr = ["J", "K"]
//打印新序列
for (i,j) in arr.enumerated() {
print("\(i):\(j)")
}
//打印結(jié)果
0:J
1:K
4.返回最大最小值 min(), max()
> 示例
min(2, 6) //返回 2
max(1, 3, 8) //返回 9
排序 sorted (sort)
> 示例
let arr = ["X", "Y", "Z"]
//默認(rèn)排序(升序)
let arr 1 = arr.sorted()
print(arr1)
//打印結(jié)果
["X", "Y", "Z"]
//自定義排序(降序)
let arr2 = ary.sorted {
$1 < $0
}
print(arr2)
//打印結(jié)果
["Z", "Y", "X"]
6.map 函數(shù)
> 示例
let arr = [2,1,3]
//數(shù)組元素進(jìn)行2倍放大
let doubleArr = arr.map {$0 * 2}
print(doubleArr)
//打印結(jié)果
[4, 2, 6]
//數(shù)組Int轉(zhuǎn)String
let moneyArr = arr.map { "￥\($0 * 2)"}
print(moneyArr)
//打印結(jié)果
["￥4", "￥2", "￥6"]
//數(shù)組轉(zhuǎn)成元組
let groupArr = arr.map {($0, "\($0)")}
print(groupArr)
//打印結(jié)果
[(2, "2"), (1, "1"), (3, "3")]
7.flapMap 函數(shù)
> 示例
let arr = [["B", "A", "C"], ["1","5"]]
//flapMap函數(shù)會(huì)降低維度
let flapMapArr = arr.flatMap{$0}
print(flapMapArr)
//打印結(jié)果
["B", "A", "C", "1", "5"] // 二維數(shù)組變成了一維
8.篩選函數(shù) filter
> 示例
let numbers = [1, 2, 3, 4, 5, 6]
//獲取偶數(shù)值
let evens = numbers.filter{$0 % 2 == 0}
print(evens)
//打印結(jié)果
[2, 4, 6]
9.reduce 函數(shù)
> 示例
let arr = [1, 2, 4]
//對(duì)數(shù)組各元素求和
let sum = arr.reduce(0) {$0 + $1}
print(sum)
//打印結(jié)果
7
//對(duì)數(shù)組各元素求積
let product = arr.reduce(1) {$0 * $1}
print(product)
//打印結(jié)果
8
10.在編程中經(jīng)常會(huì)用到的一些函數(shù)
1. abs(-1) == 1 //獲取絕對(duì)值
2. ["1","6","4"].contains("2") == false //判斷序列是否包含元素
3. ["a","b"].dropLast() == ["a"] //剔除最后一個(gè)元素
4. ["a","b"].dropFirst() == ["b"] //剔除第一個(gè)元素
5. ["a","b"].elementsEqual(["b","a"]) == false //判斷序列是否相同
6. ["a","b"].indices == 0..<2 //獲取index(indices是index的復(fù)數(shù))
7. ["A", "B", "C"].joined(separator: ":") == "A:B:C" //將序列以分隔符串聯(lián)起來(lái)成為字符串
8. Array([2, 7, 0].reversed()) == [0, 7, 2] //逆序，注意返回的并非原類型序列
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