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。

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

1 + 2       // equals 3
5 - 3 // equals 2
2 * 3 // equals 6
10.0 / 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

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

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!"
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