Generics in PHP experiment

example.php

<?php

require __DIR__ . '/TypedList.php';

class Foo {}

$list = new MrClay\Generics\TypedList('Foo');
/* @var Foo[] $list */

$list[] = new Foo();

$list[] = new stdClass(); // exception at run-time, but better than nothing

TypedArray.php

<?php

namespace MrClay\Generics;

use Exception;
use InvalidArgumentException;

class TypedList extends \SplDoublyLinkedList
{
    /**
     * @var string
     */
    protected $type;

    /**
     * @param $type string|array
     *
     * @throws InvalidArgumentException
     */
    public function __construct($type = null)
    {
        if (is_string($type)) {
            $this->setType($type);
        } elseif (is_array($type)) {
            if (empty($type)) {
                throw new InvalidArgumentException('$type cannot be empty');
            }
            foreach ($type as $val) {
                $this->push($val);
            }
        } else {
            throw new InvalidArgumentException('$type must be a class/interface name, or non-empty array of objects');
        }
    }

    /**
     * @param string $type
     *
     * @throws Exception
     */
    public function setType($type)
    {
        if (! $this->type || ($this->type === $type)) {
            $this->type = $type;
        } else {
            throw new Exception('Once set, type cannot be changed');
        }
    }

    /**
     * @return string
     */
    public function getType()
    {
        return $this->type;
    }

    /**
     * @param object $val
     *
     * @throws \InvalidArgumentException
     */
    protected function verifyType($val)
    {
        if ($this->type) {
            if (! $val instanceof $this->type) {
                throw new InvalidArgumentException('Given value is not an instance of ' .  $this->type);
            }
        } else {
            if (!is_object($val)) {
                throw new InvalidArgumentException('TypedArray can only accept objects');
            }
            $this->type = get_class($val);
        }
    }

    public function push($value)
    {
        $this->verifyType($value);
        parent::push($value);
    }

    public function unshift($value)
    {
        $this->verifyType($value);
        parent::unshift($value);
    }

    public function offsetSet($index, $value)
    {
        $this->verifyType($value);
        parent::offsetSet($index, $value);
    }
}