| Lists: | pgsql-hackers |
|---|
| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Peter Eisentraut <peter_e(at)gmx(dot)net> |
| Cc: | pgsql-hackers(at)postgreSQL(dot)org |
| Subject: | CREATE CAST requires immutable cast function? |
| Date: | 2002-09-01 02:42:00 |
| Message-ID: | 16732.1030848120@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
It says here that CREATE CAST insists the cast function be immutable.
This seems wrong to me, in view of the fact that we have numerous
built-in casts that don't adhere to that rule --- for example,
timestamptz(date) is not immutable because it depends on the timezone
setting.
Perhaps there's a case for prohibiting volatile casts (as opposed to
stable ones), but I don't really see it. I'd prefer to just remove
this restriction. Comments?
regards, tom lane
| From: | Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | Peter Eisentraut <peter_e(at)gmx(dot)net>, pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: CREATE CAST requires immutable cast function? |
| Date: | 2002-09-01 02:45:00 |
| Message-ID: | 200209010245.g812j0b04425@candle.pha.pa.us |
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| Lists: | pgsql-hackers |
Tom Lane wrote:
> Perhaps there's a case for prohibiting volatile casts (as opposed to
> stable ones), but I don't really see it. I'd prefer to just remove
> this restriction. Comments?
Volatile casts can blow up. I am sure that is the reasoning. ;-)
--
Bruce Momjian | http://candle.pha.pa.us
pgman(at)candle(dot)pha(dot)pa(dot)us | (610) 359-1001
+ If your life is a hard drive, | 13 Roberts Road
+ Christ can be your backup. | Newtown Square, Pennsylvania 19073
| From: | Peter Eisentraut <peter_e(at)gmx(dot)net> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | pgsql-hackers(at)postgreSQL(dot)org |
| Subject: | Re: CREATE CAST requires immutable cast function? |
| Date: | 2002-09-03 18:53:03 |
| Message-ID: | Pine.LNX.4.44.0209031900390.1157-100000@localhost.localdomain |
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| Lists: | pgsql-hackers |
Tom Lane writes:
> Perhaps there's a case for prohibiting volatile casts (as opposed to
> stable ones), but I don't really see it. I'd prefer to just remove
> this restriction. Comments?
I'm not wedded to it, I just modelled it after the SQL standard, but
evidently the volatility levels are different in detail. I would disallow
volatile casts in any case. There ought to be a minimal behavioral
contract between creators and users of types.
--
Peter Eisentraut peter_e(at)gmx(dot)net
| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Peter Eisentraut <peter_e(at)gmx(dot)net> |
| Cc: | pgsql-hackers(at)postgreSQL(dot)org |
| Subject: | Re: CREATE CAST requires immutable cast function? |
| Date: | 2002-09-03 20:09:40 |
| Message-ID: | 16219.1031083780@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
Peter Eisentraut <peter_e(at)gmx(dot)net> writes:
> I'm not wedded to it, I just modelled it after the SQL standard, but
> evidently the volatility levels are different in detail. I would disallow
> volatile casts in any case. There ought to be a minimal behavioral
> contract between creators and users of types.
Shrug ... ISTM the behavior of a type is whatever the type creator says
it should be. Whether a volatile cast is a good idea is dubious
(I can't think of any good examples of one offhand) but I don't see the
argument for having the system restrict the type creator's choices.
regards, tom lane