Итератор (iterator)

using System;
using System.Collections.Generic;
using System.Text;
using System.Threading;
using System.Linq;
using System.Threading.Tasks;

class Program
{
   static void Main(string[] args)
   {
    Library library = new Library();
    Reader reader = new Reader();
    reader.SeeBooks(library);

    Console.ReadLine();
   }
}

class Reader
{
    public void SeeBooks(Library library)
    {
        IBookIterator iterator = library.CreateNumerator();
        while(iterator.HasNext())
        {
            Book book = iterator.Next();
            Console.WriteLine(book.Name);
        }
    }
}

interface IBookIterator
{
    bool HasNext();
    Book Next();
}

interface IBookNumerable
{
    IBookIterator CreateNumerator();
    int Count {get;}
    Book this[int index] {get;}
}

class Book
{
    public string Name{get;set;}
}

class Library : IBookNumerable
{
    private Book[] books;

    public Library()
    {
        books = new Book[]
        {
            new Book{Name = "Война и мир"},
            new Book{Name = "Отцы и дети"},
            new Book{Name = "Вишневый сад"}
        };
    }

    public int Count
    {
        get{return books.Length;}
    }

    public Book this[int index]
    {
        get{return books[index];}
    }

    public IBookIterator CreateNumerator()
    {
        return new LibraryNumerator(this);
    }
}

class LibraryNumerator : IBookIterator
{
    IBookNumerable aggregate;
    int index = 0;

    public LibraryNumerator(IBookNumerable a)
    {
        aggregate = a;
    }

    public bool HasNext()
    {
        return index < aggregate.Count;
    }

    public Book Next()
    {
        return aggregate[index++];
    }
}