The Iterator design pattern useing PHP

To demonstrate the Iterator design pattern in PHP, we'll create a simple example that iterates over a collection of books. The Iterator pattern provides a way to access the elements of an aggregate object sequentially without exposing its underlying representation.

Project Structure
Book.php - Represents a single book.
BookList.php - Represents a collection of books.
BookListIterator.php - An iterator for the BookList.
index.php - Demonstrates the usage of the iterator.

Step-by-Step Creation and Explanation
1. Book.php This class represents a single book. It's a simple class with a constructor and a getter method for the book's title.

title = $title;
    }

    public function getTitle() {
        return $this->title;
    }
}

2. BookList.php This class represents a collection of Book objects. It stores books and provides methods to add or remove a book from the list.

books[] = $book;
    }

    public function removeBook(Book $book) {
        foreach ($this->books as $key => $b) {
            if ($b->getTitle() === $book->getTitle()) {
                unset($this->books[$key]);
            }
        }
        $this->books = array_values($this->books);
    }

    public function count() {
        return count($this->books);
    }

    public function getBook($index) {
        if (isset($this->books[$index])) {
            return $this->books[$index];
        }
        return null;
    }
}

3. BookListIterator.php This class implements the iterator for BookList. It allows traversing over the BookList collection.

bookList = $bookList;
    }

    public function hasNext() {
        return $this->currentBook < $this->bookList->count();
    }

    public function next() {
        return $this->bookList->getBook($this->currentBook++);
    }
}

4. index.php This file demonstrates the usage of the above classes. It creates a list of books, adds them to the BookList, and then iterates over them using BookListIterator.

addBook(new Book("1984"));
$bookList->addBook(new Book("To Kill a Mockingbird"));
$bookList->addBook(new Book("The Great Gatsby"));

// Iterate over book list
$iterator = new BookListIterator($bookList);
while ($iterator->hasNext()) {
    $book = $iterator->next();
    echo $book->getTitle() . "\n";
}

Running the Code When you run index.php, you should see the titles of the books printed one after the other:

1984
To Kill a Mockingbird
The Great Gatsby

This output demonstrates the Iterator pattern in action, allowing you to sequentially access elements of the BookList without exposing its internal structure.