Re: [yang-doctors] guideline for enum and value?

Hi,

Juergen Schoenwaelder <j.schoenwaelder@jacobs-university.de> wrote:
> On Thu, Jan 25, 2018 at 09:18:27AM +0100, Benoit Claise wrote:
> > Dear all,
> > 
> > Still busy with the RFC6087bis AD review, reviewing the enum sections now.
> > 
> > Do I recall correctly a guideline about not using "value" in enum?

I think this was a discussion on YANG 1.1, not 6087bis (but I might be
wrong).

> > Something to be inserted in RFC6087bis? At least a pros and cons discussion?
> >
> 
> I would rather say the opposite:
> 
>   YANG automatically assigns numeric values to enums if no values are
>   specified. This automatic assignment requires that (a) the order of
>   enums never changes and (b) additional enums are only appended but
>   never prepended or inserted. This is subtle and using explicit value
>   assignments, though more verbose, tends to be more robust when
>   modules are revised.

Is this a recommendation to always use the "value" statement?  I don't
think now is the right time to add such an recommendation, and I don't
think it should be recommended.  Maybe we could say something about
taking care when adding an enum, but RFC 7950, section 11, bullet 1
already says that value must not change, so we would essentially just
say that you must follow the rules of 7950.

/martin

> 
> Background:
> 
> Note that NETCONF and RESTCONF do not send the numeric values due to
> the way the XML and JSON encodings are defined. But this may be
> different for other encodings, the proposed CBOR encoding uses the
> numeric value. Some implementations do support mappings to protocols
> such as SNMP where numeric values are used.
> 
> We had a longer discussion about this when we talked about how we deal
> with timezones, which change regularly and have no natural numeric
> value. Algorithms to produce YANG enumerations from the timezone
> databases are difficult if you want to have stable numeric values.
> 
> /js
> 
> -- 
> Juergen Schoenwaelder           Jacobs University Bremen gGmbH
> Phone: +49 421 200 3587         Campus Ring 1 | 28759 Bremen | Germany
> Fax:   +49 421 200 3103         <https://www.jacobs-university.de/>
> 
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