Composite Pattern Example #php #design-patterns #composite-pattern

composite-pattern.php

<?php
abstract class Component
{
    protected $_parent;
    protected $_children;

    public function __construct()
    {
        $this->_children = new SplDoublyLinkedList();
    }

    public function __destruct()
    {
        echo "Destroying " . $this->toString() . "\n";
    }

    public function addChild(Component $child)
    {
        $child->setParent($this);
        $this->_children->push($child);
    }

    public function removeChild($index)
    {
        $this->getChild($index)->setParent(null);
        $this->_children->offsetUnset($index);
    }

    public function setParent(Component $parent=null)
    {
        $this->_parent = $parent;
    }

    public function getParent()
    {
        return $this->_parent;
    }

    public function getChild($index)
    {
        return $this->_children->offsetGet($index);
    }

    public function output()
    {
        foreach ($this->_children as $child)
            $child->output();
    }

    public function toString()
    {
        return "Component";
    }
}

class Leaf1 extends Component
{
    public function addChild(Component $child)
    {
        throw new Exception("Leaf1 cannot have children.");
    }

    public function removeChild($index)
    {
        throw new Exception("Leaf1 cannot have children.");
    }

    public function getChild($index)
    {
        throw new Exception("Leaf1 cannot have children.");
    }

    public function output()
    {
        echo "Leaf1\n";
    }

    public function toString()
    {
        return "Leaf1";
    }
}

class Leaf2 extends Component
{
    public function addChild(Component $child)
    {
        throw new Exception("Leaf2 cannot have children.");
    }

    public function removeChild($index)
    {
        throw new Exception("Leaf2 cannot have children.");
    }

    public function getChild($index)
    {
        throw new Exception("Leaf2 cannot have children.");
    }

    public function output()
    {
        echo "Leaf2\n";
    }

    public function toString()
    {
        return "Leaf2";
    }
}


class CompositeComponent extends Component
{
    public function toString()
    {
        return "CompositeComponent";
    }
}

$composite1 = new CompositeComponent();
$composite2 = new CompositeComponent();
$composite2->addChild(new Leaf1());
$composite2->addChild(new Leaf2());
$composite1->addChild($composite2);
$composite1->addChild(new Leaf1());
$composite1->output();

$child = $composite1->getChild(1);
echo "Parent of child: " . ($child->getParent() == null ? "(null)" : $child->getParent()->toString()) . "\n";
echo "Removing child from composite...\n";
$composite1->removeChild(1);
echo "Parent of child: " . ($child->getParent() == null ? "(null)" : $child->getParent()->toString()) . "\n";

$composite1->removeChild(0);
$composite1->addChild($child);
echo "Parent of child: " . ($child->getParent() == null ? "(null)" : $child->getParent()->toString()) . "\n";
//$composite2->destroyChildren();
//$composite1->detachChildren();
unset($composite1);
echo "Parent of child: " . ($child->getParent() == null ? "(null)" : $child->getParent()->toString()) . "\n";