"Rob Wilton (rwilton)" <[email protected]> wrote:
>
>
> > -----Original Message-----
> > From: Martin Björklund <[email protected]>
> > Sent: 26 February 2021 16:30
> > To: [email protected]
> > Cc: Rob Wilton (rwilton) <[email protected]>; [email protected]
> > Subject: Re: [netmod] type equivalence
> >
> > Andy Bierman <[email protected]> wrote:
> > > On Fri, Feb 26, 2021 at 7:06 AM Martin Björklund <[email protected]>
> > wrote:
> > >
> > > > "Rob Wilton \(rwilton\)" <[email protected]> wrote:
> > > > >
> > > > >
> > > > > > -----Original Message-----
> > > > > > From: netmod <[email protected]> On Behalf Of Juergen
> > > > Schoenwaelder
> > > > > > Sent: 24 February 2021 20:39
> > > > > > To: [email protected]
> > > > > > Subject: Re: [netmod] type equivalence
> > > > > >
> > > > > > Here is an attempt to come up with better wording. If people agree
> > on
> > > > > > a new wording, I volunteer to submit an errata.
> > > > > >
> > > > > > OLD
> > > > > >
> > > > > > o A "type" statement may be replaced with another "type"
> > statement
> > > > > > that does not change the syntax or semantics of the type.
> > For
> > > > > > example, an inline type definition may be replaced with a
> > > > typedef,
> > > > > > but an int8 type cannot be replaced by an int16, since the
> > syntax
> > > > > > would change.
> > > > > >
> > > > > > NEW
> > > > > >
> > > > > > o A "type" statement may be replaced with another "type"
> > statement
> > > > > > that does not change the semantics of the type or the
> > underlying
> > > > > > built-in type. For example, an inline type definition may
> > be
> > > > > > replaced with a semantically equivalent typedef derived from
> > the
> > > > > > same built-in type, but an int8 type cannot be replaced by
> > an
> > > > > > int16, since the underlying built-in type would change.
> > > >
> > >
> > >
> > > I think the NEW text captures the original intent and is OK for an
> > errata.
> >
> > +1
> >
> >
> > > I believe the use-case discussed at the time of writing was simply
> > > replacing an inline
> > > type with the identical type but within a typedef-stmt instead of
> > > inline
> > > within a leaf or leaf-list.
> > >
> > > Perhaps this rule is too strict.
> > > There is a simple way to defeat it:
> > >
> > > Change all
> > > type foo { ... }
> > > to
> > > type union {
> > > type foo { ... }
> > > }
> > >
> > > Now you can add new values and semantics without taking away the
> > original
> > > syntax and semantics.
> > >
> > > type union {
> > > type foo { ... }
> > > type bar { ... } // note new member types added at end of list
> > > }
> > >
> > > But it is not clear that this would be legal or completely BC. It
> > certainly
> > > could change the encoding in JSON and CBOR.
> >
> > It is not allowed by sec 11 in 7950, since it changes the syntax of
> > the type.
> [RW]
>
> But the proposed errata removes the text about not changing the
> syntax, or are you referring to other text?
The new text says that the built-in type cannot change, which it does
if we add a type to a union. Hmm, perhaps this isn't clear.
/martin
>
> Rob
>
>
> >
> >
> > /martin
> >
> >
> >
> > >
> > >
> > > Andy
> > >
> > >
> > > > [RW]
> > > > >
> > > > > Would the text be more clear it is just specified what is allowed,
> > e.g.,
> > > > >
> > > > > o A "type" statement may be replaced with another "type"
> > statement
> > > > > that resolves to the same underlying built-in type. For
> > example,
> > > > > ...
> > > > >
> > > > >
> > > > > What does "semantics of the type" cover?
> > > >
> > > > Suppose you have:
> > > >
> > > > typedef "timestamp" {
> > > > type yang:date-time;
> > > > description
> > > > "The time that an event occurred";
> > > > }
> > > >
> > > > then you can't change it to:
> > > >
> > > > typedef "timestamp" {
> > > > type yang:date-time;
> > > > description
> > > > "The time that an event was received.";
> > > > }
> > > >
> > > > The syntax is the same, but the semantics are different.
> > > >
> > > >
> > > > /martin
> > > >
> > > >
> > > >
> > > >
> > > > >
> > > > > If I have this type:
> > > > >
> > > > > typedef "timestamp" {
> > > > > type "string";
> > > > > description
> > > > > "The time of day that an event occurred, in any format";
> > > > > }
> > > > >
> > > > > then can I replace it with this definition:
> > > > >
> > > > > typedef "timestamp" {
> > > > > type "string";
> > > > > description
> > > > > "The time of day, and optionally date, that an event
> > > > > occurred, in any format";
> > > > > }
> > > > >
> > > > >
> > > > >
> > > > > Tangentially, it is worth noting the RFC 8342 also writes about
> > syntactic
> > > > > constraints covering types:
> > > > >
> > > > > 5.3. The Operational State Datastore (<operational>)
> > > > >
> > > > > Syntactic constraints MUST NOT be violated, including
> > hierarchical
> > > > > organization, identifiers, and type-based constraints. If a node
> > in
> > > > > <operational> does not meet the syntactic constraints, then it
> > > > > MUST NOT be returned, and some other mechanism should be used to
> > flag
> > > > > the error.
> > > > >
> > > > > I'm not sure how clear RFC 8342 section 5.3 is about returning
> > values
> > > > > that can be represented by the underlying built-in-type, but are
> > outside
> > > > > the value space defined by a range, length, or pattern statement.
> > > > >
> > > > > My memory during the discussions was that it is allowed to return a
> > value
> > > > > outside arange, length, pattern statement, as long as it is
> > contained
> > > > > in the value space of the built-in-type. E.g., cannot return 257 in
> > a
> > > > > uint8, but can return 11 even if the type range is 1..10.
> > > > >
> > > > > But, I'm not sure that is what the text actually states.
> > > > >
> > > > > Regards,
> > > > > Rob
> > > > >
> > > > >
> > > > > >
> > > > > > /js
> > > > > >
> > > > > > On Mon, Feb 22, 2021 at 03:20:02PM +0100, Carsten Bormann wrote:
> > > > > > > On 2021-02-22, at 15:17, Juergen Schoenwaelder
> > > > <j.schoenwaelder@jacobs-
> > > > > > university.de> wrote:
> > > > > > > >
> > > > > > > > I guess considering the built-in types as incompatible is the
> > most
> > > > > > > > robust approach. If we agree that RFC 7950 tried to say this,
> > we
> > > > could
> > > > > > > > file an errata and propose clearer language.
> > > > > > >
> > > > > > > Right. And we can keep the COMI key-to-URL mapping as is, as
> > this
> > > > > > clarification is necessary for its correct functioning.
> > > > > > >
> > > > > > > Grüße, Carsten
> > > > > > >
> > > > > >
> > > > > > --
> > > > > > 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/>
> > > > > >
> > > > > > _______________________________________________
> > > > > > netmod mailing list
> > > > > > [email protected]
> > > > > > https://www.ietf.org/mailman/listinfo/netmod
> > > > >
> > > > > _______________________________________________
> > > > > netmod mailing list
> > > > > [email protected]
> > > > > https://www.ietf.org/mailman/listinfo/netmod
> > > >
> > > > _______________________________________________
> > > > netmod mailing list
> > > > [email protected]
> > > > https://www.ietf.org/mailman/listinfo/netmod
> > > >
_______________________________________________
netmod mailing list
[email protected]
https://www.ietf.org/mailman/listinfo/netmod
