public static function is_assoc($arr)
	{
		if ( ! is_array($arr))
		{
			throw new \InvalidArgumentException('The parameter must be an array.');
		}

		$counter = 0;
		foreach ($arr as $key => $unused)
		{
			if ( ! is_int($key) or $key !== $counter++)
			{
				return true;
			}
		}
		return false;
	}