Re: domain usage

Bruno Wolff III <bruno(at)wolff(dot)to> writes:
> I have a question about the use of domains in 7.3.
> Will I be able to use them to catch mistakes in doing comparisons
> or value setting between objects with the same underlying type but
> in different domains (without doing an explicit type cast)?

No, I don't think so. It certainly doesn't work at the moment:

regression=# create domain d1 int4;
CREATE DOMAIN
regression=# create domain d2 int4;
CREATE DOMAIN
regression=# select '1'::d1 = '1'::d2;
?column?
----------
t
(1 row)

The reason it doesn't work is that d1 and d2 are treated as
binary-compatible with int4, so the int4 = operator is found and
applied.

If we did not have this binary-compatibility behavior, domains would be
near useless, because out-of-the-box they'd have no applicable functions
or operators at all. Do you want to have to issue a ton of CREATE
FUNCTION and CREATE OPERATOR commands for every domain you make?

regards, tom lane