Protocols

1. Giới thiệu

Protocol định nghĩa blueprint của methods, properties và requirements.

2. Khai báo Protocol

protocol Drawable {
    func draw()
}

struct Circle: Drawable {
    func draw() {
        print("Drawing circle")
    }
}

struct Square: Drawable {
    func draw() {
        print("Drawing square")
    }
}

3. Property Requirements

protocol Named {
    var name: String { get }
    var fullName: String { get set }
}

struct Person: Named {
    var name: String
    var fullName: String
}

4. Method Requirements

protocol Togglable {
    mutating func toggle()
}

struct Switch: Togglable {
    var isOn = false

    mutating func toggle() {
        isOn.toggle()
    }
}

5. Initializer Requirements

protocol Initializable {
    init(value: Int)
}

class MyClass: Initializable {
    var value: Int

    required init(value: Int) {
        self.value = value
    }
}

6. Protocol Inheritance

protocol Animal {
    var name: String { get }
}

protocol Pet: Animal {
    var owner: String { get }
}

struct Dog: Pet {
    var name: String
    var owner: String
}

7. Default Implementation

protocol Greetable {
    var name: String { get }
    func greet()
}

extension Greetable {
    func greet() {
        print("Hello, \(name)!")
    }
}

struct Person: Greetable {
    var name: String
    // greet() có implementation mặc định
}

8. Protocol as Type

func render(_ drawable: Drawable) {
    drawable.draw()
}

let shapes: [Drawable] = [Circle(), Square()]
shapes.forEach { $0.draw() }

9. Protocol Composition

protocol Named { var name: String { get } }
protocol Aged { var age: Int { get } }

func celebrate(_ person: Named & Aged) {
    print("Happy \(person.age)th birthday, \(person.name)!")
}

struct Person: Named, Aged {
    var name: String
    var age: Int
}

10. Common Protocols

// Equatable
struct Point: Equatable {
    var x: Int
    var y: Int
}
Point(x: 1, y: 2) == Point(x: 1, y: 2)  // true

// Hashable
struct Person: Hashable {
    var name: String
}

// Codable
struct User: Codable {
    var id: Int
    var name: String
}

// CustomStringConvertible
struct Item: CustomStringConvertible {
    var description: String { "Item" }
}

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📝 Tóm tắt

• Protocol định nghĩa contract
• { get } và { get set } cho properties
• Extension cung cấp default implementation
• Protocol composition với &
• Dùng như type cho polymorphism
• Common: Equatable, Hashable, Codable