Multiple Inheritance in PHP

multiple_inheritance_example.php

<?php
/**
 * Abomination class implementing multiple inheritance via
 * __call magic method
 */
abstract class MultipleInheritance
{
    /**
     * List of parent classes
     * 
     * @var array
     * @access protected
     */
    protected $_parents = array();    

    /**
     * List of parent objects - generated automatically
     * 
     * @var array
     * @access private
     */
    private $_parentObjects = array();

    /**
     * Constructor (thank you captain Obvious :)
     * 
     * - init the parent objects
     * 
     * @access public
     */
    public function __construct()
    {
        foreach ($this->_parents as $parentClass) {
            $this->_parentObjects []= new $parentClass();
        }
    }

    /**
     * __call magic method
     * 
     * @param string $name 
     * @param array $arguments 
     * @access public
     * @return mixed
     */
    public function __call($name, array $arguments)
    {
        foreach ($this->_parentObjects as $object) {
            if (is_callable(array($object, $name))) {
                return call_user_func_array(array($object, $name), $arguments);
            }
        }

        throw new Exception('No such method: ' . $name);
    }

    /**
     * __set magic method
     * 
     * @param string $key 
     * @param mixed $value 
     * @access public
     * @return void
     */
    public function __set($key, $value)
    {
        foreach ($this->_parentObjects as $object) {
            // isset() misses null properties
            if (property_exists($object, $key)) {
                $object->{$key} = $value;
                return;
            }

            // property_exists() misses magic properties
            if (isset($object, $key)) {
                $oject->{$key} = $value;
                return;
            }
        }
    }

    /**
     * __get magic method
     * 
     * @param string $key 
     * @access public
     * @return mixed
     */
    public function __get($key)
    {
        foreach ($this->_parentObjects as $object) {
            if (property_exists($object, $key) || @$object->{$key}) {
                return $object->{$key};
            }
        }
    }

    /**
     * Check inheritance
     * 
     * @param string $class 
     * @access public
     * @return bool
     */
    public function isInstanceOf($class)
    {
        if (in_array($class, $this->_parents)) {
            return true;
        }

        foreach ($this->_parentObjects as $parent) {
            if ($parent instanceof MultipleInheritance) {
                if ($parent->isInstanceOf($class)) {
                    return true;
                }
            }
        }

        return false;
    }
}

/**
 * Example classes: 
 */
class Dad 
{
    public $familyName = 'Smith';

    /**
     * Can parallel park
     * 
     * @access public
     * @return void
     */
    public function park()
    {
        echo 'Look, I can parallel park' . PHP_EOL;
    }    

    /**
     * Can ground the kids
     * 
     * @access public
     * @return void
     */
    public function ground()
    {
        echo 'Grounded by DAD' . PHP_EOL;
    }
}

class GrandMa
{
    public $familyName = 'Doe';

    /**
     * Knows bed-time stories
     * 
     * @access public
     * @return void
     */
    public function tellStory()
    {
        echo 'When I was your age...' . PHP_EOL;
    }

    /**
     * __isset 
     * 
     * @param string $key 
     * @access public
     * @return bool
     */
    public function __isset($key)
    {
        if ($key == 'ancientCraft') {
            return true;
        }
    }

    /**
     * __get 
     * 
     * @param string $key 
     * @access public
     * @return mixed
     */
    public function __get($key)
    {
        if ($key == 'ancientCraft') {
            return 'knit';
        }
    }
}

class Mom extends MultipleInheritance
{
    protected $_parents = array('GrandMa');


    /**
     * Makes sandwiches
     * 
     * @access public
     * @return void
     */
    public function makeSandwich()
    {
        echo 'Just making a sandwich' . PHP_EOL;
    }    

    /**
     * Can grounds the kids
     * 
     * @access public
     * @return void
     */
    public function ground()
    {
        echo 'Grounded by MOM' . PHP_EOL;
    }
}


class Child extends MultipleInheritance
{
    protected $_parents = array('Dad', 'Mom');
}

/*
Let's try it out:
*/
$child = new Child();
$child->park(); // inherited from Dad
$child->makeSandwich(); // inherited from Mom
$child->ground(); // inherited from both, but the method in the Dad class will execute
$child->tellStory(); // inherited from GrandMd


if ($child->isInstanceOf('Mom')) {
    echo get_class($child) . ' class inherits from Mom' . PHP_EOL; 
} else {
    echo get_class($child) . ' class does not inherit from Mom' . PHP_EOL;
}

if ($child->isInstanceOf('GrandMa')) {
    echo get_class($child) . ' class inherits from GrandMa' . PHP_EOL;
} else {
    echo get_class($child) . ' class does not inherit from GrandMa' . PHP_EOL;
}

/**
 * Stranger class
 */
class Stranger {}

if ($child->isInstanceOf('Stranger')) {
    echo get_class($child) . ' class inherits from Stranger' . PHP_EOL;
} else {
    echo get_class($child) . ' class does not inherit from Stranger' . PHP_EOL;
}

echo 'The child\'s family name is ' . $child->familyName . PHP_EOL;
if ($child->ancientCraft) {
    echo 'The child knows to ' . $child->ancientCraft . PHP_EOL;
}