final protected static function verifyAll(array $expressions, $type = __CLASS__)
    {
        foreach ($expressions as $key => $expression) {
            if (!($expression instanceof $type)) {
                throw new PinqException(
                        'Invalid array of expressions: invalid expression of type %s at index %s, expecting %s',
                        Utilities::getTypeOrClass($expression),
                        $key,
                        $type);
            }
        }

        return $expressions;
    }