Example for http://codefuss.calepin.co/a-simple-entity-engine-in-php.html

entityengine.php

<?php
class EntityEngine
{
    private $components = array();
    
    /**
     * @param Entity $entity
     * @param string $componentName
     * @return Component
     */
    public function getComponent(Entity $entity, $componentName)
    {
        if($this->hasComponent($entity, $componentName)) {
            return $this->components[$componentName][$entity->getId()];
        }
        
        return null;
    }
    
    /**
     * @param Entity $entity
     * @param string $componentName
     * @return boolean
     */
    public function hasComponent(Entity $entity, $componentName)
    {
        return isset($this->components[$componentName][$entity->getId()]);
    }
    
    /**
     * @param Entity $entity
     * @param Component $component 
     */
    public function setComponent(Entity $entity, Component $component)
    {
        $this->components[$component->getName()][$entity->getId()] = $component;
    }
    
    /**
     * @param string $componentName
     * @return array of Component
     */
    public function getAll($componentName)
    {
        if(! isset($this->components[$componentName])) {
            return array();
        }
        
        return $this->components[$componentName];
    }
}

interface Entity
{
    /**
     * @return unique identifier for this instance
     */
    public function getId();
    
    /**
     * @param string $component
     * @return Component
     */
    public function getComponent($componentName);
    
    /**
     * @param Component $component
     */
    public function setComponent(Component $component);
}

abstract class SimpleEntity implements Entity
{
    private $engine;
    
    /**
     * @param EntityEngine $engine 
     */
    public function __construct(EntityEngine $engine)
    {
        $this->engine = $engine;
    }
    
    public function getId()
    {
        return spl_object_hash($this);
    }
    
    public function getComponent($componentName)
    {
        return $this->engine->getComponent($this, $componentName);
    }
    
    public function setComponent(Component $component)
    {
        $this->engine->setComponent($this, $component);
    }
}

interface Component
{
    public function getName();
}

// Component Implementations of the Examples

class DialogComponent implements Component
{
    public function getName() 
    {
        return "Dialog";
    }
    
    public function moveRight();
}

class CollisionComponent implements Component
{
    public function getName() 
    {
        return "Collision";
    }

    public function update();
}