快看Sample代码，速学Swift语言（3）-运算符

运算符是用来检查，更改或组合值的特殊符号或短语。Swift提供的很多常规的运算符，如+、-、*、/、%、=、==等，以及逻辑运算的&&、||等等，基本上不需要重复介绍，我们在这里只需要了解一些不太一样的运算符就可以了。如Swift引入的新运算符，范围操作符号，包括..<和...两个，该随笔介绍Swift常规的运算符中，以及和其他语言有所差异的部分。

赋值运算符

let b = 10
var a = 5
a = b
// a is now equal to 10

赋值语句，处理和其他语言一样。

1 2	`let` `(x,` `y) = (1,` `2)` `// x is equal to 1, and y is equal to 2`

这种代码是类似ECMAScript 6的脚本写法，通过把右边元祖对象解构赋值给左边对应的参数。

数学运算符

+ 2       // equals 3
- 3       // equals 2
* 3       // equals 6
0 / 2.5  // equals 4.0

这些都是和其他语言没有什么不同，循例列出参考下

对于字符，也可以使用+符号进行连接新的字符串

1	`"hello, "` `+` `"world"` `// equals "hello, world"`

一元操作符中的-、+运算，和算术里面的负负得正，正负得负的意思一样了。

let three = 3
let minusThree = -three       // minusThree equals -3
let plusThree = -minusThree   // plusThree equals 3, or "minus minus three"

1 2	`let` `minusSix` `= -6` `let` `alsoMinusSix` `= +minusSix` `// alsoMinusSix equals -6`

组合运算符提供+= 、-=的运算符操作

var a = 1
a += 2
// a is now equal to 3

对比运算符和其他语言差不多

等于 (a == b)
不等于 (a != b)
大于 (a > b)
小于 (a < b)
大于等于 (a >= b)
小于等于 (a <= b)

另外值得注意的是，Swift提供了对比引用的两个操作符号，=== 和 !==，用来检查两个引用是否完全相等；或者不相等的。而==只是用来对比两个对象的值是否一致。

== 1   // true because 1 is equal to 1
!= 1   // true because 2 is not equal to 1
> 1    // true because 2 is greater than 1
< 2    // true because 1 is less than 2
>= 1   // true because 1 is greater than or equal to 1
<= 1   // false because 2 is not less than or equal to 1

对比运算符也经常用来If条件语句里面

let name = "world"
if name == "world" {
    print("hello, world")
} else {
    print("I'm sorry \(name), but I don't recognize you")
}
// Prints "hello, world", because name is indeed equal to "world".

三元运算符

三元运算符？：和C#里面表现是一样的

1	`question` `?` `answer1` `:` `answer2`

let contentHeight = 40
let hasHeader = true
let rowHeight = contentHeight + (hasHeader ? 50 : 20)

空值转换操作符

空值转换符是对可空类型（可选类型）的一个值得转换出来(a ?? b)。

let defaultColorName = "red"
var userDefinedColorName: String?   // defaults to nil
  
var colorNameToUse = userDefinedColorName ?? defaultColorName
// userDefinedColorName is nil, so colorNameToUse is set to the default of "red"

userDefinedColorName = "green"
colorNameToUse = userDefinedColorName ?? defaultColorName
// userDefinedColorName is not nil, so colorNameToUse is set to "green"

范围操作符

闭合范围运算符 ... 和半闭合范围运算符 ..< 两个

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

半闭合的范围运算符

let names = ["Anna", "Alex", "Brian", "Jack"]
let count = names.count
for i in 0..<count {
    print("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

或者如下使用

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

以及一侧范围的运算符，包括左侧和右侧两个部分

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

let range = ...5
range.contains(7)   // false
range.contains(4)   // true
range.contains(-1)  // true

逻辑运算符

let allowedEntry = false
if !allowedEntry {
    print("ACCESS DENIED")
}
// Prints "ACCESS DENIED"

let enteredDoorCode = true
let passedRetinaScan = false
if enteredDoorCode && passedRetinaScan {
    print("Welcome!")
} else {
    print("ACCESS DENIED")
}
// Prints "ACCESS DENIED"

let hasDoorKey = false
let knowsOverridePassword = true
if hasDoorKey || knowsOverridePassword {
    print("Welcome!")
} else {
    print("ACCESS DENIED")
}
// Prints "Welcome!"

if enteredDoorCode && passedRetinaScan || hasDoorKey || knowsOverridePassword {
    print("Welcome!")
} else {
    print("ACCESS DENIED")
}
// Prints "Welcome!"

或者使用括号使之更加方便阅读

if (enteredDoorCode && passedRetinaScan) || hasDoorKey || knowsOverridePassword {
    print("Welcome!")
} else {
    print("ACCESS DENIED")
}
// Prints "Welcome!"