interface IAnimal {
    eat() : void;
}

class Dog implements IAnimal {
    eat() : void {
        console.log("Dog eats");
    }
}

class Cat implements IAnimal {
    eat() : void {
        console.log("Cat eats");
    }
}

class Owner {
    feed(animal: IAnimal) : void {
        animal.eat();
    }
}

// driver code below
const dog = new Dog();
const cat = new Cat();
dog.eat();
cat.eat();

const owner = new Owner();
owner.feed(dog);
owner.feed(cat);