Symfony\Component\PropertyAccess\PropertyAccessor::readIndex PHP Method

    private function readIndex($zval, $index)
    {
        if (!$zval[self::VALUE] instanceof \ArrayAccess && !is_array($zval[self::VALUE])) {
            throw new NoSuchIndexException(sprintf('Cannot read index "%s" from object of type "%s" because it doesn\'t implement \ArrayAccess.', $index, get_class($zval[self::VALUE])));
        }

        $result = self::$resultProto;

        if (isset($zval[self::VALUE][$index])) {
            $result[self::VALUE] = $zval[self::VALUE][$index];

            if (!isset($zval[self::REF])) {
                // Save creating references when doing read-only lookups
            } elseif (is_array($zval[self::VALUE])) {
                $result[self::REF] = &$zval[self::REF][$index];
            } elseif (is_object($result[self::VALUE])) {
                $result[self::REF] = $result[self::VALUE];
            }
        }

        return $result;
    }