Re: [GENERAL] Needed function IF(expr, expr, expr)

Rod Taylor <rbt@rbt.ca> writes:
>> Any comments on the UNKNOWN issue?  It's not too late to change that for
>> 7.4, if we have consensus that we should.

> I would actually prefer to get UNKNOWN so I can apply my own default
> type, but we're not even given the chance to resolve the unknown issue
> ourselves.

> CREATE OR REPLACE FUNCTION if(bool,anyelement,anyelement)
> RETURNS anyelement
> AS 'SELECT
>      CASE WHEN $2 is of (unknown) THEN
>             CASE WHEN $1 THEN $2::point ELSE $3::point END
>           ELSE
>             CASE WHEN $1 THEN $2 ELSE $3 END
>           END' language SQL;

There's no chance of that working --- the parser has to be able to
determine the result type of a function invocation without reference
to the function body.  (Otherwise CREATE OR REPLACE FUNCTION invalidates
every use of the function.)

I don't feel that the anyelement in -> anyelement out mechanism is the
last word in polymorphism, though.  Care to propose additional features
of the same kind?  If you can find a way to describe the behavior you
want in terms of the function signature, it'd be worth considering ...

            regards, tom lane