using System;

​

// Add the missing code to Chicken and Egg so the following actions are completed:

// •    Chicken implements the IBird interface.

// •    A Chicken lays an egg that will hatch into a new Chicken.

// •    Eggs from other types of birds should hatch into a new bird of their parent type.

// •    Hatching an egg for the second time throws a System.InvalidOperationException.

​

public interface IBird<TBird>

    where TBird : IBird<TBird>

{

    IEgg<TBird> Lay();

}

​

public interface IEgg<TBird>

    where TBird : IBird<TBird>

{

    TBird Hatch();

}

​

public class Chicken : IBird<Chicken>

{

    public IEgg<Chicken> Lay()

    {

        return new Egg<Chicken>(() => new Chicken());

    }

}

​

public class Duck : IBird<Duck>

{

    public IEgg<Duck> Lay()

    {

        return new Egg<Duck>(() => new Duck());

    }

}

​

public class Egg<TBird> : IEgg<TBird>

    where TBird : IBird<TBird>

{

    private Func<TBird> createBird;

    private bool hatched;

​

    public Egg(Func<TBird> createBird)

    {

        this.createBird = createBird;

    }

​

    public TBird Hatch()

    {

        if (hatched) throw new System.InvalidOperationException("Egg was already hatched");

        hatched = true;

        return createBird();

    }

}

​

public class Program

{

    public static void Main(string[] args)

    {

        var chicken1 = new Chicken();

        var egg = chicken1.Lay();

        var childChicken = egg.Hatch();

    }

}