Re: [netmod] Pattern statements [was Re: Query about augmenting module from submodule in YANG 1.0]

[Juergen Schoenwaelder <[e-mail]>]

On Wed, Aug 23, 2017 at 02:23:12PM +0100, Robert Wilton wrote:
> 
> 1) Email address.  I understand that the full regex to validate all email
> addresses is very complex, but checking that it at least contains an @
> symbol still has benefit.  It would seem that a short imperfect regex is
> better than a complete perfect regex.

What is your definition of 'better'? A stricter pattern catches more
errors. An imperfect pattern is better than none.

> 2) A list of VLAN ranges, e.g. want to allow strings that look like this:
> "1-10,20-400,600,2000-3000", but only with non overlapping values in
> ascending order.  It is easy to write a regex to check that the structure is
> right, but AFAIK it is hard (impossible?) to write a regex that ensures that
> the ranges don't overlap and are specified in ascending order.

So what. Does this provide a helpful argument whether patterns should
be strict or imperfect?

> So, I propose that we use regexes for checking that the string is
> structurally correct, but don't use regexes to perform numerical range
> checks of string encoded numbers, since it makes the regexes hard to
> read/verify, and doesn't improve the readability of the YANG file either.

So here is the point I think:

   It is desirable that regexes are as strict as they can be.
   However, if regexes become so complicated that they become a
   verification and maintenance problem by themself, then less strict
   regexes may be a better choice.

/js

-- 
Juergen Schoenwaelder           Jacobs University Bremen gGmbH
Phone: [phone]         Campus Ring 1 | 28759 Bremen | Germany
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