Re: Casting from a domain

On Fri, Mar 04, 2005 at 03:40:17PM -0500, Tom Lane wrote:
> "Jim C. Nasby" <decibel(at)decibel(dot)org> writes:
> > decibel=# create cast (interval as rrs.seconds) WITH FUNCTION rrs.interval_to_seconds(interval) AS IMPLICIT;
> > CREATE CAST
> > decibel=# select cast('1 month'::interval AS seconds);
> > ERROR: cannot cast type interval to seconds
>
> Given the current coercion rules, we should probably disallow attempts
> to define casts that involve domains. Casts are on base types. The
> down-cast from a domain to its base type is hardwired, and the up-cast
> from base type to domain is too (with invocation of any constraints
> that may apply). Adding random user-defined casts to this would
> probably just create confusion and ambiguity. In particular, this
> was already meaningless:
>
> decibel=# create domain rrs.seconds as double precision;
> CREATE DOMAIN
> decibel=# create cast (double precision as rrs.seconds) WITHOUT FUNCTION AS IMPLICIT;
> CREATE CAST
>
> since the presence of the cast might be thought to justify coercing
> floats to "seconds" without invoking domain constraints.

Yeah, I figured it was probably an issue with it being a domain. I was
looking for a way to do this without the extra work involved in defining
a full-blown type. I guess the good news is I should be able to re-use
all the double-precision functions and what-not for 'seconds'.

BTW, is there a reason 'double' isn't an alias for 'double precision'?
I'm pretty sure every other database I've used (other than oracle of
course) supports 'double'. " precision" is just too much extra typing
after all... :P
--
Jim C. Nasby, Database Consultant decibel(at)decibel(dot)org
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