Mise en application du Patron Visiteur avec Doctrine2

Book.php

<?php

namespace Entity;

/**
* Le livre est l'élément visité.
* De cette manière on peut lui apliquer des traitements sans affecter sa structure tout en gardant la séparation Modèle/Controlleur
*/
class Book implements \Reader\Element
{
    
    //...
    
    /**
     * The part of Visitor Pattern
     *
     * @param Reader\Visitor $visitor
     */
    public function accept(\Reader\Visitor $visitor)
    {
        $visitor->visit($this);
    }
}

BookVisitor.php

<?php
namespace Reader;

/**
 * Description of BookVisitor
 */
class BookVisitor implements Visitor {
    
    protected $book, $line = 0;
    
    public function visit(Element $element)
    {
        $this->book = $element;
    }

    //...
}

BookVisitor.read.php

<?php
namespace Reader;

/**
 * Description of BookVisitor
 */
class BookVisitor implements Visitor {
    
    //...

    /**
     * Example : this method does not impact Book structure 
     * 
     * read book content line by line
     * 
     * @return string
     */
    public function read()
    {
        $content    = $this->book->getContent();
        $a_line     = explode("\n", $content);
        
        if(!count($a_line))
        {
            throw new \RuntimeException('Where is the book?!');
        }
        
        if(isset($a_line[$this->line]))
        {
            $ret = $a_line[$this->line];
            $this->line++;
            return $ret;
        }
        
        return 'The End';
    }
}

Client.php

<?php

namespace Controller;

/**
 * Description of Client
 */
class Client {
    
    public function action()
    {
        //get the Book from Doctrine
        // ... 
        $book =  new \Entity\Book();
        $book->setContent("#Hello world\n ## this line should not be read at the first time");
        //
        
        $visitor = new \Reader\BookVisitor();
        $visitor->visit($book);
        
        //Here we go
        echo $visitor->read();
    }
}