Re: Prefered Types

03.05.2011 23:06, Tom Lane пишет:
> I wrote:
>> Alvaro Herrera<alvherre(at)commandprompt(dot)com> writes:
>>> The interesting discussion is what happens next. To me, this is all
>>> related to this previous discussion:
>>> http://archives.postgresql.org/pgsql-hackers/2010-09/msg00232.php
>> Yeah, there doesn't seem like much point unless we have a clear idea
>> what we're going to do with the change.
> BTW, it occurs to me to wonder whether, instead of making types be more
> or less preferred, we should attack the issue from a different direction
> and assign preferred-ness ratings to casts. That seems to be more or
> less the direction that Robert was considering in the above-linked
> thread. I'm not sure it's better than putting the ratings on types ---
> in particular, neither viewpoint seems to offer a really clean answer
> about what to do when trying to resolve a multiple-argument function
> in which one possible resolution offers a more-preferred conversion for
> one argument but a less-preferred conversion for another one. But it's
> an alternative we ought to think about before betting all the chips on
> generalizing typispreferred.
>
> Personally I've always felt that the typispreferred mechanism was a bit
> of a wart; changing it from a bool to an int won't improve that, it'll
> just make it a more complicated wart. Casts have already got a
> standards-blessed notion that some are more equal than others, so
> maybe attaching preferredness ratings to them will be less of a wart.
> Not sure about it though.
>
> regards, tom lane
>
Now I use this change i manual change preferring of some types (in
system tables) and it give me possibility not add some functions clones.
I don`t know how (and i think i have no right) to change syntax to use
this feature.
After many times thinking i find another way to resolve my problem:
if function only one we must use Assignment cast rules.
But it can help only for me... thats why i think we can change rules to
calc prefer like
assignment rules have lesser priority, but available.
but here we can see problem like
F(smallint)
F(integer)
but call like F(float)
i wouldn`t like to fail it.

PS This patch needet, because in any case we must calc prefer more
smartly, yes this patch is 1/10 of full solution, but it`s first step!!!

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