Interfaces in Swift

protocol Speaker {
    func speak()
}
class Dog: Speaker {
    func speak() {
        print("Woof")
    }
}

Full lesson:

An interface defines what a class can do, not how it does it or what it is. A Truck, a Robot, and a Drone aren't the same kind of thing — but they can all move(). You'd put move() in a Movable protocol and have each one adopt it.

Interface vs abstract class

A class inherits from at most one parent class but can adopt many protocols. That's why protocols are the right tool for cross-cutting capabilities like Comparable, Equatable, Codable, Sequence, etc.

The language landscape

• Swift — the keyword is protocol. A class lists the protocols it adopts after its name (and after its superclass, if it has one), separated by commas; structs and enums can adopt protocols too.
• C# / Java — first-class interface keyword. C# uses : for both inheritance and implementation; Java uses extends for inheritance and implements for interfaces.
• Python — no separate interface; abstract base classes (ABCs) with all-abstract methods serve the same role.
• JavaScript — no interface keyword in plain JS (TypeScript has it). The convention is a stub class.
• C++ — a class with only pure-virtual methods is an interface. Multiple inheritance lets a class implement several.

Your task

The Speaker protocol is already declared. Create a Dog class that adopts it, with a speak() method that prints "Woof".

Expected output:

Woof