Message-ID: <475AE32C.9040201@acm.org>
Date: Sat, 08 Dec 2007 10:32:12 -0800
From: TJ O'Donnell <tjo@acm.org>
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To: Tom Lane <tgl@sss.pgh.pa.us>
CC: PostgreSQL - SQL <pgsql-sql@postgresql.org>
Subject: Re: polymorphic functions and domains
References: <47584418.1020204@acm.org> <5167.1196988696@sss.pgh.pa.us>
In-Reply-To: <5167.1196988696@sss.pgh.pa.us>
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I'm not sure I can propose a scheme that would
work in all situations, but one could simply
considered the built-in data type underlying
the domain.  In my case, this would mean deciding
between character varying and bytea, which seems to
work just fine.

As far as surprising behavior, isn't the scheme
for casting literals already prone to surprises?

TJ

Tom Lane wrote:
> "TJ O'Donnell" <tjo@acm.org> writes:
>> I really want two polymorphic functions, one taking
>> a domain data type using varchar and one bytea.
> 
> These aren't polymorphic functions, actually; they're just overloaded.
> 
>> In that case, postgres complains that it cannot decide
>> which one to use when called with the
>> untyped literal 'abc'.
> 
> Yeah, functions taking domains as arguments are problematic.  I believe
> that with the current resolution rules, a function taking a domain can
> only "win" an ambiguous-function comparison if it's an exact match
> to the input types --- which in this case means you have to cast the
> literal to the domain type.
> 
> There's been some talk of trying to rejigger the resolution rules to
> make them more friendly to functions that're declared to take domains,
> but no one's put forward any concrete proposal.  It's not at all clear
> to me how to do it without introducing a lot of surprising behavior :-(
> 
> 			regards, tom lane