Role.php

<?php

namespace DesignPatterns\Visitor;

/**
 * Visitor Pattern
 *
 * Purpose:
 * The Visitor Pattern lets you outsource operations on objects to other objects. The main reason to do this is to keep
 * a separation of concerns. But classes have to define an contract to allow visitors (the "accept" method in the example below).
 * 
 * The contract is an abstract class but you can have also a clean interface. 
 * In that case, each Visitor has to choose itself which method to invoke on the visitor.
 */
abstract class Role
{
    /**
     * This method handles a double dispatch based on the short name of the Visitor
     *
     * Feel free to override it if your object must call another visiting behavior
     *
     * @param \DesignPatterns\Visitor\RoleVisitorInterface $visitor
     *
     * @throws \InvalidArgumentException
     */
    public function accept(RoleVisitorInterface $visitor)
    {
        // this trick to simulate double-dispatch based on type-hinting
        $klass = get_called_class();
        preg_match('#([^\\\\]+)$#', $klass, $extract);
        $visitingMethod = 'visit' . $extract[1];

        // this ensures strong typing with visitor interface, not some visitor objects
        if (!method_exists(__NAMESPACE__ . '\RoleVisitorInterface', $visitingMethod)) {
            throw new \InvalidArgumentException("The visitor you provide cannot visit a $klass instance");
        }

        call_user_func(array($visitor, $visitingMethod), $this);
    }
}