Swift 是基于 Apache 2.0 协议开源。
Swift 可以在 Linux 上运行，并且使用 Clang/LLVM 编译器。

• 强类型、静态类型、编译型、类型安全
• 使用自动引用计数 (ARC) 来管理内存
• 面向对象编程
  • 面向协议编程，其实就是面向对象中的接口
• 函数式编程

protocol Vehicle {
    func drive()
}

protocol Electric: Vehicle {
    func charge()
}

struct ElectricCar: Electric {
    func drive() {
        print("Electric car is driving")
    }

    func charge() {
        print("Charging electric car")
    }
}

关键字

以下是一个表格，列出了 Swift 中的所有关键字，并将它们按类别分类：

数据类型

// 整数类型
var age: Int = 20

// 浮点数类型
var weight: Double = 65.5

// 字符串类型
var name: String = "Alice"

// 布尔类型
var isPassed: Bool = true

// 数组类型
var scores: [Int] = [85, 90, 78, 92]

// 字典类型
var studentInfo: [String: Any] = [
    "name": "Alice",
    "age": 20,
    "scores": [85, 90, 78, 92]
]

// 元组类型
var student: (name: String, age: Int, scores: [Int]) = ("Alice", 20, [85, 90, 78, 92])

// 可选类型
var grade: String? = "A"
var address: String? = nil // 没有地址

逻辑控制

// if 语句
if age >= 18 {
    print("\(name) is an adult.")
} else {
    print("\(name) is a minor.")
}

// switch 语句
switch grade {
case "A":
    print("\(name) has excellent grades!")
case "B":
    print("\(name) has good grades.")
default:
    print("\(name) needs improvement.")
}

// for-in 循环
for score in scores {
    print("Score: \(score)")
}

// while 循环
var index = 0
while index < scores.count {
    print("Score at index \(index): \(scores[index])")
    index += 1
}

运算符

// 算术运算符
let sum = 5 + 3       // 加法
let difference = 5 - 3 // 减法
let product = 5 * 3    // 乘法
let quotient = 5 / 3   // 除法
let remainder = 5 % 3  // 取余

// 比较运算符
let isEqual = (5 == 3) // 等于
let isGreater = (5 > 3) // 大于
let isLess = (5 < 3)    // 小于

// 逻辑运算符
let isTrue = true
let isFalse = false
let andResult = isTrue && isFalse // 与运算
let orResult = isTrue || isFalse  // 或运算
let notResult = !isTrue           // 非运算

函数

// 计算平均分
func calculateAverage(scores: [Int]) -> Double {
    let total = scores.reduce(0, +)
    return Double(total) / Double(scores.count)
}

// 判断是否及格
func isPassing(average: Double) -> Bool {
    return average >= 60
}

// 使用函数
let averageScore = calculateAverage(scores: scores)
print("Average score: \(averageScore)")

if isPassing(average: averageScore) {
    print("\(name) passed the exam.")
} else {
    print("\(name) failed the exam.")
}

面向对象编程

// 定义一个类
class Student {
    var name: String
    var age: Int
    var scores: [Int]

    // 初始化方法
    init(name: String, age: Int, scores: [Int]) {
        self.name = name
        self.age = age
        self.scores = scores
    }

    // 方法：计算平均分
    func calculateAverage() -> Double {
        let total = scores.reduce(0, +)
        return Double(total) / Double(scores.count)
    }

    // 方法：判断是否及格
    func isPassing() -> Bool {
        return calculateAverage() >= 60
    }
}

// 创建对象
let student1 = Student(name: "Alice", age: 20, scores: [85, 90, 78, 92])

// 使用类的方法
let average = student1.calculateAverage()
print("Average score of \(student1.name): \(average)")

if student1.isPassing() {
    print("\(student1.name) passed the exam.")
} else {
    print("\(student1.name) failed the exam.")
}