Casting from a domain

I'm trying to create a seconds domain that is an interval 'mashed to
seconds' as I once saw Tom describe it.

decibel=# create domain rrs.seconds as double precision;
CREATE DOMAIN
decibel=# create cast (double precision as rrs.seconds) WITHOUT FUNCTION AS IMPLICIT;
CREATE CAST
decibel=# create function rrs.interval_to_seconds(interval) returns seconds as 'SELECT extract( EPOCH FROM $1 );' LANGUAGE SQL;
CREATE FUNCTION
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

\dC shows that the cast is there, and rrs.interval_to_seconds works as
expected, and according to \df does return seconds.

Version is 7.4.5.
--
Jim C. Nasby, Database Consultant decibel(at)decibel(dot)org
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