Swift — Protocols

Basic protocol

protocol Drawable {
    func draw()
}

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

Protocol with properties

protocol Named {
    var name: String { get }
}

protocol Aged {
    var age: Int { get }
}

class Person: Named, Aged {
    var name: String
    var age: Int

    init(name: String, age: Int) {
        self.name = name
        self.age = age
    }
}

Protocol with default implementation

protocol Greetable {
    func greet()
}

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

struct Robot: Greetable {
    // Uses default implementation
}

Robot().greet() // Hello!

Protocol inheritance

protocol Printable {
    func printInfo()
}

protocol Loggable: Printable {
    func log()
}

class Document: Loggable {
    func printInfo() { print("Printing document") }
    func log() { print("Logging document") }
}

Protocol extensions

protocol Collection {
    var count: Int { get }
    var isEmpty: Bool { get }
}

extension Collection {
    var isEmpty: Bool { count == 0 }
}

Mini Practice

Write Swift code that:

1. Defines a protocol with properties and methods
2. Adds a default implementation with an extension
3. Uses protocol inheritance
4. Creates a protocol extension

Up Next

In the next lesson, you'll learn about Optionals — handling missing values.