Re: [netmod] type equivalence

[Martin Björklund <[e-mail]>]

Andy Bierman <[e-mail]> wrote:
> On Fri, Feb 26, 2021 at 7:06 AM Martin Björklund <[e-mail]> wrote:
> 
> > "Rob Wilton \(rwilton\)" <rwilton=[e-mail]> wrote:
> > >
> > >
> > > > -----Original Message-----
> > > > From: netmod <[e-mail]> On Behalf Of Juergen
> > Schoenwaelder
> > > > Sent: 24 February 2021 20:39
> > > > To: [e-mail]
> > > > 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.


/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: [phone]         Campus Ring 1 | 28759 Bremen | Germany
> > > > Fax:   [phone]         <https://www.jacobs-university.de/>
> > > >
> > > > _______________________________________________
> > > > netmod mailing list
> > > > [e-mail]
> > > > https://www.ietf.org/mailman/listinfo/netmod
> > >
> > > _______________________________________________
> > > netmod mailing list
> > > [e-mail]
> > > https://www.ietf.org/mailman/listinfo/netmod
> >
> > _______________________________________________
> > netmod mailing list
> > [e-mail]
> > https://www.ietf.org/mailman/listinfo/netmod
> >