IteratorPattern.swift

import Foundation

protocol Iterator {
    func hasNext() -> Bool
    func next() -> AnyObject
}

protocol Aggregate {
    func iterator() -> Iterator
}

class Book {
    var name: String?
    
    init(name: String) {
        self.name = name
    }
}

class BookShelf: Aggregate {
    private var books: [Book] = []

    var length: Int {
        get {
            return books.count
        }
    }
    
    func getBookAt(index: Int) -> Book {
        return books[index]
    }
    func appendBook(book: Book) {
        self.books.append(book)
    }
    func iterator() -> Iterator {
        return BookShelfIterator(bookShelf: self)
    }
}

class BookShelfIterator: Iterator {
    private var bookShelf: BookShelf
    private var index = 0
    
    init(bookShelf: BookShelf) {
        self.bookShelf = bookShelf
    }
    func hasNext() -> Bool {
        if self.index < bookShelf.length {
            return true
        } else {
            return false
        }
    }
    func next() -> AnyObject {
        return bookShelf.getBookAt(self.index++)
    }
}

print("Program start ...")
let bookShelf = BookShelf()
bookShelf.appendBook(Book(name: "Around the World in 80 Days"))
bookShelf.appendBook(Book(name: "Bible"))
bookShelf.appendBook(Book(name: "Cinderella"))
bookShelf.appendBook(Book(name: "Around the World in 80 Days"))
bookShelf.appendBook(Book(name: "Daddy-Long-Legs"))

let itr = bookShelf.iterator()
while itr.hasNext() {
    let book = itr.next() as! Book
    if let n = book.name {
        print(n)
    }
}