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iOS Swift 語法 底層原理 與 內存管理分析 專題：【iOS Swift5語法】

00 - 匯編
01 - 基礎語法
02 - 流程控制
03 - 函數(shù)
04 - 枚舉
05 - 可選項
06 - 結構體和類
07 - 閉包
08 - 屬性
09 - 方法
10 - 下標
11 - 繼承
12 - 初始化器init
13 - 可選項

目錄

• 01-if-else
• 02-while
• 03-for
• 04-for-區(qū)間運算符用在數(shù)組上
• 05-區(qū)間類型
• 06-帶間隔的區(qū)間值
• 07-switch
• 08-fallthrough
• 09-switch注意點
• 10-復合條件
• 11-區(qū)間匹配、元組匹配
• 12-值綁定
• 13-where
• 14-標簽語句

01-if-else

• if后面的條件可以省略小括號
• 條件后面的大括號不可以省略
• 與操作可以用逗號或者&&, 或操作可以用||
• 逗號可以用來可選項綁定

let age = 28
if age >= 22, age < 30 {
    print("Gat married")
} else if age >= 18 {
    print("Being a adult")
} else if age >= 7 {
    print("Go to school")
} else {
    print("Just a child")
}

• 條件后面的大括號不可以省略

// 報錯: Expected '{' after 'if' condition
if age > 100
    print("age > 100")

• if后面的條件只能是Bool類型

if age {    // error: cannot convert value of type 'Int' to expected condition type 'Bool'

}

02-while

• Swift3開始,去除了自增(++), 自減(--)運算符

// while
var num = 5
while num > 0 {
    print("num is \(num)")
    num -= 1
}// 打印了5次

• repeat-while相當于C語言中的do-while
  • repeat-while至少執(zhí)行1次

var num2 = -1
repeat {
    print("num2 is \(num2)")
} while num2 > 0

03-for

• 閉區(qū)間運算符...

let names = ["Anna", "Alex", "Brian", "Jack"]
for i in 0...3 {
    print(names[i])
}  // Anna Alex Brian Jack

print("----------")

let range = 1...3
for i in range {
    print(names[i])
}  // Alex Brian Jack

print("----------")

let a = 1
var b = 2
for i in a...b {
    print(names[i])
}  // Alex Brian

print("----------")
for i in  a...3 {
    print(names[i])
}  // Alex Brian Jack

• for 接收參數(shù)默認聲明為let,可以聲明為var

// i默認是let, 有需要時可以聲明為var
for var i in 1...3 {
    i += 5
    print(i)
}  // 6 7 8

• 使用下劃線_忽略

// _ 忽略
for _ in 1...3 {
    print("for")
}  // for for for

• 半開區(qū)間運算符

// - 半開區(qū)間運算符: a..<b , 取值 a <= 取值 < b
for i in 1..<5 {
    print(i)
}  // 1 2 3 4

04-for-區(qū)間運算符用在數(shù)組上

let names = ["Anna", "Alex", "Brian", "Jack"]
for name in names[0...3] {
    print(name)
} // Anna Alex Brian Jack

• 單側區(qū)間: 讓區(qū)間朝一個方向盡可能的遠

for name in names[2...] {
    print(name)
} // Brian Jack

for name in names[...2] {
    print(name)
} // Anna Alex Brian

for name in names[..<2] {
    print(name)
} // Anna Alex

• 判斷是否在區(qū)間內

let range = ...5
range.contains(7)   // false
range.contains(4)   // true
range.contains(-3)  // true

05-區(qū)間類型

• 閉區(qū)間類型ClosedRange

// 閉區(qū)間
let range1: ClosedRange<Int> = 1...3

• 區(qū)間類型Range

let range2: Range<Int> = 1..<3

• 半開區(qū)間類型PartialRangeThrough

let range3: PartialRangeThrough<Int> = ...5

• 字符、字符串也能使用區(qū)間運算符,但默認不能用在for-in中

let stringRange1 = "cc"..."ff"  // ClosedRange<String>
stringRange1.contains("cb") // false
stringRange1.contains("dz") // true
stringRange1.contains("fg") // false

let stringRange2 = "a"..."f"    // ClosedRange<String>
stringRange2.contains("d")  // true
stringRange2.contains("h")  // false

• 字符區(qū)間必須指明Character類型, 否則編譯器自動推導為String類型

// \0到~包括了所有可能要用到的ASCII字符
// 定義字符區(qū)間必須指明Character類型,否則編譯器自動推導為String類型
let characterRange: ClosedRange<Character> = "\0"..."~"
characterRange.contains("G")    // true

06-帶間隔的區(qū)間值

• stride定義

///   - start: 從start值開始
///   - through: 依次累加through
///   - stride: 到stride結束,不超過stride
public func stride<T>(from start: T, through end: T, by stride: T.Stride) -> StrideThrough<T> where T : Strideable

let hours = 11
let hourInterval = 2
// tickMark的取值: 從4開始, 累加2, 不超過11
for tickMark in stride(from: 4, through: hours, by: hourInterval) {
    print(tickMark)
}   // 4 6 8 10

07-switch

• case default后面不能寫大括號{}

• default后面至少有一條語句,不能寫分號,因為分號不是語句。通常沒有其他處理就用break

var number = 2
switch number {
case 1:
    print("number is 1")
    break
case 2:
    print("number is 2")
    break
case 3:
    print("number is 3")
    break
default:
    break   // default后面至少有一條語句,不能寫分號,因為分號不是語句
    //    print("number is \(number)")
}   // number is 2

• case默認可以不寫break, 并不會貫穿到后面的條件

var number1 = 1
switch number1 {
case 1:
    print("number1 is 1")
case 2:
    print("number1 is 2")
default:
    print("number1 is other")
} // number1 is 1

08-fallthrough

• 使用fallthrough可以實現(xiàn)貫穿效果

var number = 1
switch number {
case 1:
    print("number is 1")
    fallthrough
case 2:
    print("number is 2")
default:
    break
}
// number is 1
// number is 2

09-switch注意點

• switch必須要保證能處理所有情況

// error: switch must be exhaustive
var number = 1
switch number {
case 1:
    print("number is 1")
case 2:
    print("number is 2")
}

• case、default后面至少要有一條語句

如果不想做任何事,加個break即可

var number = 1
switch number {
case 1:
    print("number is 1")
case 2:
    print("number is 2")
default:
    break
}

• 如果能保證已處理所有情況, 也可以不必使用default

enum Answer {case right, wrong}
let answer = Answer.right
switch answer {
case Answer.right:
    print("right")
case Answer.wrong:
    print("wrong")
}

// 由于已確定answer是Answer類型,因此可以省略Answer
switch answer {
case .right:
    print("right")
case .wrong:
    print("wrong")
}

10-復合條件

• switch也支持Character、String類型

let string = "Jack"
switch string {
case "Jack":
    fallthrough    // 貫穿
case "Rose":
    print("Right person")
default:
    break
} // Right person

// 等價于上面
switch string {
case "Jack", "Rose":
    print("Right person")
default:
    break
} // Right person

let character: Character = "a"
switch character {
case "a", "A":
    print("The letter A")
default:
    print("Not the letter A")
}  // The letter A

11-區(qū)間匹配、元組匹配

• swift區(qū)間條件匹配

let count = 62
switch count {
case 0:
    print("none")
case 1..<5:
    print("a few")
case 5..<12:
    print("several")
case 12..<100:
    print("dozens of")
case 100..<1000:
    print("hundreds of")
default:
    print("many")
} // dozens of

• 可以使用下劃線_忽略某個值

let point = (1, 1)
switch point {
case (0, 0):
    print("the origin")
case (_, 0):
    print("on the x-axis")
case (0, _):
    print("on the y-axis")
case (-2...2, -2...2):
    print("inside the box")
default:
    print("outside of the box")
} // inside the box

12-值綁定

值綁定就是將相應的值 綁定到常量/變量。值綁定默認為let, 必要時let也可以改為var

let point = (2, 0)
switch point {
case (let x, 0):
    print("on the x-axis with an x value of \(x)")
case (0, let y):
    print("on the y-axis with an y value of \(y)")
case (let x, let y):
    print("somewhere else at (\(x), \(y))")
}
// on the x-axis with an x value of 2

13-where

• where 條件過濾

• where在switch中使用

let point = (1,-1)
switch point {
case let (x, y) where x == y:
    print("on the line x == y")
case let (x, y) where x == -y:
    print("on the line x == -y")
case let (x, y):
    print("(\(x), \(y)) is just some arbitrary point")
} // on the line x == -y

• where在for-in中使用

// 將所有正數(shù)加起來
var numbers = [10, 20, -10, -20, 30, -30]
var sum = 0
for number in numbers where number > 0 {
    sum += number
}
print(sum)  // 60

14-標簽語句

• 使用continue, break 進行標簽跳轉

outer: for i in 1...4 {
    for k in 1...4 {
        if k == 3 {
            continue outer
        }
        if i == 3 {
            break outer
        }
        print("i == \(i), k == \(k)")
    }
}
// i == 1, k == 1
// i == 1, k == 2
// i == 2, k == 1
// i == 2, k == 2

iOS Swift 語法 底層原理 與 內存管理分析 專題：【iOS Swift5語法】

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