Swift 基本语法学习笔记

变量和常量

变量使用 var 关键字声明，常量使用 let 关键字声明。

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var myVariable = 42
myVariable = 50
let myConstant = 42

类型注解

你可以在变量或常量后面加上冒号和类型名称，以标注该变量或常量的类型。

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var myVariable: Double = 42
myVariable = 50
let myConstant: Float = 42

数组和字典

数组使用方括号包含值，字典使用中括号包含键值对。

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var someInts = [Int]()
someInts.append(3)
someInts = []

var someDict = [String: Int]()
someDict["one"] = 1
someDict = [:]

控制流

Swift 提供了传统的控制流结构，例如 for 循环和 switch 语句，以及增强版的控制流结构，例如 for-in 循环和 switch 语句的匹配模式。

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let individualScores = [75, 43, 103, 87, 12]
var teamScore = 0
for score in individualScores {
    if score > 50 {
        teamScore += 3
    } else {
        teamScore += 1
    }
}
print(teamScore)

let interestingNumbers = [
    "Prime": [2, 3, 5, 7, 11, 13],
    "Fibonacci": [1, 1, 2, 3, 5, 8],
    "Square": [1, 4, 9, 16, 25],
]
var largest = 0
for (kind, numbers) in interestingNumbers {
    for number in numbers {
        if number > largest {
            largest = number
        }
    }
}
print(largest)

可选类型

在 Swift 中，当一个变量或常量可能为空时，你可以将它声明为可选类型。如果值存在，则可选类型包含该值；如果值不存在，则可选类型为空。

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var optionalString: String? = "Hello"
print(optionalString == nil)

var optionalName: String? = "John Appleseed"
var greeting = "Hello!"
if let name = optionalName {
    greeting = "Hello, \(name)"
} else {
    greeting = "Hello, anonymous"
}
print(greeting)

函数和闭包

Swift 支持函数闭包，可以在其中定义一个代码块并进行传递。

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func greet(person: String, day: String) -> String {
    return "Hello \(person), today is \(day)."
}
print(greet(person: "Bob", day: "Tuesday"))

let numbers = [1, 2, 3, 4, 5]
let mappedNumbers = numbers.map({ number in 3 * number })
print(mappedNumbers)

结构体和类

Swift 支持结构体和类，这两种类型可以定义方法和属性。

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class Shape {
    var numberOfSides = 0
    func simpleDescription() -> String {
        return "A shape with \(numberOfSides) sides."
    }
}

var shape = Shape()
shape.numberOfSides = 7
var shapeDescription = shape.simpleDescription()

枚举和 switch 语句

Swift 支持枚举类型，并提供 switch 语句来匹配枚举值。

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enum Rank: Int {
    case ace = 1
    case two, three, four, five, six, seven, eight, nine, ten
    case jack, queen, king
    func simpleDescription() -> String {
        switch self {
        case .ace:
            return "ace"
        case .jack:
            return "jack"
        case .queen:
            return "queen"
        case .king:
            return "king"
        default:
            return String(self.rawValue)
        }
    }
}

let ace = Rank.ace
let aceRawValue = ace.rawValue
print(ace.simpleDescription())

以上就是本文介绍的 Swift 基本语法，希望对你的学习有所帮助。