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Thread: CREATE CAST too strict?

CREATE CAST too strict?

From
Peter Eisentraut
Date:
I noticed that some of the entries in pg_cast are shaped in a way that CREATE 
CAST wouldn't let pass.  For example, the cast from cidr to varchar is 
effectively defined as

CREATE CAST (cidr AS varchar) WITH FUNCTION text(inet) AS ASSIGNMENT;

but CREATE CAST wouldn't allow this because the argument type of the function 
doesn't match the source type of the cast and the return type of the function 
doesn't match the target type.  (These are two separate tests.)

I propose that we relax these two checks to test for binary-coercibility 
instead, which is effectively what is expected and required here anyway.

The application is that I would like to create alias types for compatibility 
that have a different name but behave mostly like an existing type.  For that 
I would like to reuse a few of these cast functions.  Pretty much exactly how 
text vs. varchar is handled.  Citext might actually also benefit.

Re: CREATE CAST too strict?

From
Peter Eisentraut
Date:
Am Mittwoch, 9. Juli 2008 schrieb Peter Eisentraut:
> I propose that we relax these two checks to test for binary-coercibility
> instead, which is effectively what is expected and required here anyway.

Here is the corresponding patch.

Re: CREATE CAST too strict?

From
Tom Lane
Date:
Peter Eisentraut <peter_e@gmx.net> writes:
> Am Mittwoch, 9. Juli 2008 schrieb Peter Eisentraut:
>> I propose that we relax these two checks to test for binary-coercibility
>> instead, which is effectively what is expected and required here anyway.

> Here is the corresponding patch.

Looks good, but you might want to add a sentence to the documentation
pointing out that the function result type has to match the cast target
type; that seems not to be explicitly stated anywhere.

I also notice that the CREATE CAST page is still worded as if "binary
compatible" were a symmetric relationship, which it is not.  We probably
need to rework it a bit; but that's not really related to this patch.
        regards, tom lane

Re: CREATE CAST too strict?

From
Bruce Momjian
Date:
Peter, have you completed this yet?

---------------------------------------------------------------------------

Peter Eisentraut wrote:
> Am Mittwoch, 9. Juli 2008 schrieb Peter Eisentraut:
> > I propose that we relax these two checks to test for binary-coercibility
> > instead, which is effectively what is expected and required here anyway.
> 
> Here is the corresponding patch.

[ Attachment, skipping... ]

> 
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--  Bruce Momjian  <bruce@momjian.us>        http://momjian.us EnterpriseDB
http://enterprisedb.com
 + If your life is a hard drive, Christ can be your backup. +

Re: CREATE CAST too strict?

From
Peter Eisentraut
Date:
On Friday 22 August 2008 22:25:08 Bruce Momjian wrote:
> Peter, have you completed this yet?

yes

>
> ---------------------------------------------------------------------------
>
> Peter Eisentraut wrote:
> > Am Mittwoch, 9. Juli 2008 schrieb Peter Eisentraut:
> > > I propose that we relax these two checks to test for
> > > binary-coercibility instead, which is effectively what is expected and
> > > required here anyway.
> >
> > Here is the corresponding patch.
>
> [ Attachment, skipping... ]
>
> > --
> > Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org)
> > To make changes to your subscription:
> > http://www.postgresql.org/mailpref/pgsql-hackers
>
> --
>   Bruce Momjian  <bruce@momjian.us>        http://momjian.us
>   EnterpriseDB                             http://enterprisedb.com
>
>   + If your life is a hard drive, Christ can be your backup. +