Dominik Liebler 032cc57cf6 cs Visitor
2013-09-12 11:20:10 +02:00

41 lines
1.5 KiB
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);
}
}