/**

* 访问者模式

*

* 表示一个作用于某对象结构中的各元素的操作,可以在不改变各元素的类的前提下定义作用于这些元素的新操作

*

*/

abstract class Visitor

{

abstract public function visitCroncreteElementA($element);

abstract public function visitCroncreteElementB($element);

}

class ConcreteVisitor1 extends Visitor

{

public function visitCroncreteElementA($element)

{

echo get_class($element)." visit 1A
";

}

public function visitCroncreteElementB($element)

{

echo get_class($element)." visit 1B
";

}

}

class ConcreteVisitor2 extends Visitor

{

public function visitCroncreteElementA($element)

{

echo get_class($element)." visit 2A
";

}

public function visitCroncreteElementB($element)

{

echo get_class($element)." visit 2B
";

}

}

abstract class Element

{

abstract public function accept($visitor);

}

class ConcreteElementA extends Element

{

public function accept($visitor)

{

$visitor->visitCroncreteElementA($this);

}

}

class ConcreteElementB extends Element

{

public function accept($visitor)

{

$visitor->visitCroncreteElementB($this);

}

}

class ObjectStructure

{

private $_elements = array();

public function attach($element)

{

$this->_elements[] = $element;

}

public function detach($element)

{

if($key = array_search($element,$this->_elements) !== false) unset($this->_elements[$key]);

}

public function accept($visitor)

{

foreach($this->_elements as $element)

{

$element->accept($visitor);

}

}

}

//

$objOS = new ObjectStructure();

$objOS->attach(new ConcreteElementA());

$objOS->attach(new ConcreteElementB());

$objCV1 = new ConcreteVisitor1();

$objCV2 = new ConcreteVisitor2();

$objOS->accept($objCV1);

$objOS->accept($objCV2);