Struct

1. Giới thiệu

Struct là value type dùng để định nghĩa custom data types.

2. Khai báo Struct

struct Person {
    var name: String
    var age: Int
}

var person = Person(name: "Alice", age: 25)
print(person.name)  // Alice

3. Memberwise Initializer

struct Point {
    var x: Double
    var y: Double
    // Swift tự động tạo init(x:y:)
}

let point = Point(x: 10, y: 20)

4. Custom Initializer

struct Rectangle {
    var width: Double
    var height: Double

    init(width: Double, height: Double) {
        self.width = width
        self.height = height
    }

    init(side: Double) {
        self.width = side
        self.height = side
    }
}

let rect = Rectangle(width: 10, height: 20)
let square = Rectangle(side: 5)

5. Computed Properties

struct Circle {
    var radius: Double

    var area: Double {
        return .pi * radius * radius
    }

    var circumference: Double {
        return 2 * .pi * radius
    }
}

let circle = Circle(radius: 5)
print(circle.area)  // 78.54...

6. Methods

struct Counter {
    var count = 0

    mutating func increment() {
        count += 1
    }

    mutating func reset() {
        count = 0
    }

    func describe() -> String {
        return "Count is \(count)"
    }
}

var counter = Counter()
counter.increment()
print(counter.describe())

7. Static Properties và Methods

struct Math {
    static let pi = 3.14159

    static func square(_ n: Double) -> Double {
        return n * n
    }
}

print(Math.pi)
print(Math.square(5))

8. Value Type Semantics

struct Point {
    var x: Int
    var y: Int
}

var point1 = Point(x: 10, y: 20)
var point2 = point1  // Copy được tạo

point2.x = 100

print(point1.x)  // 10 (không thay đổi)
print(point2.x)  // 100

9. Conform to Protocols

struct Person: Codable, Hashable {
    let name: String
    let age: Int
}

// Codable cho JSON
let person = Person(name: "Alice", age: 25)
let data = try! JSONEncoder().encode(person)

// Hashable cho Set/Dictionary
var people: Set<Person> = [person]

10. Ví dụ thực tế

struct User: Codable {
    let id: Int
    let name: String
    let email: String

    var displayName: String {
        name.isEmpty ? "Unknown" : name
    }

    func validate() -> Bool {
        return !name.isEmpty && email.contains("@")
    }
}

struct APIResponse<T: Codable>: Codable {
    let status: Int
    let data: T?
    let message: String?
}

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📝 Tóm tắt

• Struct là value type (copy on assign)
• Memberwise initializer tự động
• mutating cho methods thay đổi self
• static cho type-level members
• Phổ biến cho models, DTOs
• Conform Codable cho JSON