Design Patterns - An example of php composition pattern related questions

<code><?php
abstract class MenuComponent
{
    abstract function add(MenuComponent $component);
    abstract function remove(MenuComponent $component);
    abstract function getName();
    abstract function displayOperation();

}

class MenuComposite extends MenuComponent
{
    private $_items = array(); 
    private $_name = null;

    function __construct($name)
    {
        $this->_name = $name;
    }

    function remove(MenuComponent $component){

    }

    function add(MenuComponent $component)
    {
        $this->_items[$component->getName()] = $component;
    }

    function getName(){
        return $this->_name;
    }

     public function displayOperation() {  
        static $align = '|';  

            $align .='';  
        
        echo $this->_name, " <br/>";  
        foreach($this->_items as $name=> $item) {  
            echo $align;  
            $item->displayOperation();  
        }  
    }  
}

class Client
{
    static function displayMenu()
    {
        $subMenu1 = new MenuComposite('submenu1');
        $subMenu1->add($subMenu1);
        $subMenu1->displayOperation();
    }
}

Client::displayMenu();</code>

The output is an infinite loop
submenu1
|submenu1
|submenu1
...

Why is this happening? After the first recursive call to displayOperation(), the foreach should be empty and then stop. Why is there an infinite loop?

Reply content:

<code><?php
abstract class MenuComponent
{
    abstract function add(MenuComponent $component);
    abstract function remove(MenuComponent $component);
    abstract function getName();
    abstract function displayOperation();

}

class MenuComposite extends MenuComponent
{
    private $_items = array(); 
    private $_name = null;

    function __construct($name)
    {
        $this->_name = $name;
    }

    function remove(MenuComponent $component){

    }

    function add(MenuComponent $component)
    {
        $this->_items[$component->getName()] = $component;
    }

    function getName(){
        return $this->_name;
    }

     public function displayOperation() {  
        static $align = '|';  

            $align .='';  
        
        echo $this->_name, " <br/>";  
        foreach($this->_items as $name=> $item) {  
            echo $align;  
            $item->displayOperation();  
        }  
    }  
}

class Client
{
    static function displayMenu()
    {
        $subMenu1 = new MenuComposite('submenu1');
        $subMenu1->add($subMenu1);
        $subMenu1->displayOperation();
    }
}

Client::displayMenu();</code>

The output is an infinite loop
submenu1
|submenu1
|submenu1
...

Why is this happening? After the first recursive call to displayOperation(), the foreach should be empty and then stop. Why is there an infinite loop?

Implementation of

add $this->_items[$component->getName()] = $component;

Note$subMenu1->add($subMenu1);

The attribute $_items["submenu1"] of instance $subMenu1 is itself $subMenu1

Then it goes on endlessly...

The class attribute $this->item is always the object you instantiate and pass in, so the displayOperation() method keeps looping