Interfaces in Scala

trait Speaker {
    def speak(): Unit
}
class Dog extends Speaker {
    override def speak(): Unit = {
        println("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 trait and have each one implement it.

Interface vs abstract class

A class inherits from at most one parent class but can implement many interfaces. That's why interfaces are the right tool for cross-cutting capabilities like Comparable, Serializable, Iterable, etc.

The language landscape

• C# / Java — first-class interface keyword. C# uses : for both inheritance and implementation; Scala uses extends for both a parent class and the first trait, then with for further traits (there is no implements).
• Python — no separate interface; abstract base classes (ABCs) with all-abstract methods serve the same role.
• Scala — no interface keyword; a trait with abstract methods plays that role, and a class can mix in several traits.
• C++ — a class with only pure-virtual methods is an interface. Multiple inheritance lets a class implement several.

Your task

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

Expected output:

Woof