To: "Roger Moloney" <ramoloney@hotmail.com>
cc: pgsql-interfaces@postgresql.org
Subject: Re: plpgsql: defuault parameters and constant function parameters 
In-reply-to: <BAY115-F27A40D39CE453718AA0380AFD30@phx.gbl> 
References: <BAY115-F27A40D39CE453718AA0380AFD30@phx.gbl>
Comments: In-reply-to "Roger Moloney" <ramoloney@hotmail.com>
	message dated "Tue, 28 Aug 2007 12:31:57 -0000"
Date: Wed, 29 Aug 2007 20:19:23 -0400
Message-ID: <13701.1188433163@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>

"Roger Moloney" <ramoloney@hotmail.com> writes:
> Having just done the first draft of a large migration from informix to 
> postgres, I wanted to point out that the migration was hugely complicated by 
> postgres inability to define default parameters

You can get that effect using function name overloading.  For instance

create function f(x int, y int) ...

create function f(x int) ... as 'select f(x, 1)' ...

It's easier if the defaultable parameters are at the end, but I rather
wonder how your informix system is disambiguating the calls either
with a signature like that.  If you leave off just one of the two
defaultable parameters, how does it know which?

>       I dont want to make them output parameters as they are not output 
> parameters. I am returning different output parameters. However it would be 
> great if I could modify (and not pass back) the value of a input parameter. 

Just use a differently named local variable, perhaps?  Actually, because
of the scoping rules it seems to me to work fine even if they have the
same name:

regression=# create function ff(f1 int) returns int as $$
declare f1 int := coalesce(f1, 1);
begin
  return f1;
end$$ language plpgsql;
CREATE FUNCTION
regression=# select ff(3);
 ff 
----
  3
(1 row)

regression=# select ff(null);
 ff 
----
  1
(1 row)

> Any chance of allowing input parameters to be modified within the function 
> body ?

That check is there to prevent mistakes, and I think it's a good one.

			regards, tom lane