using System;

using System.Collections.Generic;

​

class Pet

{

    public Pet(string name)

    {

        Name = name;

    }

    public string Name { get; private set; }

}

​

class Dog : Pet

{

    public Dog(string name) : base(name) {}

}

​

class Cat : Pet

{

    public Cat(string name) : base(name) {}

}

​

// Covariance:

​

void PrintPetNames(IEnumerable<Pet> pets)

{

    Console.WriteLine("Pet names: ");

    foreach(var pet in pets)

        Console.Write(pet.Name + " ");

}

​

IEnumerable<Pet> petDogs = new List<Dog>

{

    new Dog("Fido"), new Dog("Rover")

};

​

IEnumerable<Pet> petCats = new List<Cat>

{

    new Cat("Wiskers"), new Cat("Fluffy")

};

​

PrintPetNames(petDogs);

PrintPetNames(petCats);