Обсуждение: variadic flag doesn't work with "any" type

Hello

There is missing expansion for variadic parameter from any array to
real parameters when variadic type is "any".

It can be solved on C level, but in this moment we have not a access
to parser, so we don't know, if variadic flag was used or not.

Regards

Pavel Stehule

Pavel Stehule <pavel.stehule@gmail.com> writes:
> There is missing expansion for variadic parameter from any array to
> real parameters when variadic type is "any".

That's not a bug, it's intentional.  Variadic any is intended to let the
C function accept any old parameter list.  We should not assume that we
should do something special with a parameter that happens to be an array.

Possibly variadic anyarray will do what you are after.

            regards, tom lane

2010/12/9 Tom Lane <tgl@sss.pgh.pa.us>:
> Pavel Stehule <pavel.stehule@gmail.com> writes:
>> There is missing expansion for variadic parameter from any array to
>> real parameters when variadic type is "any".
>
> That's not a bug, it's intentional. =C2=A0Variadic any is intended to let=
 the
> C function accept any old parameter list. =C2=A0We should not assume that=
 we
> should do something special with a parameter that happens to be an array.
>
> Possibly variadic anyarray will do what you are after.

I didn't explain it well, sorry

so I have a function foo(variadic "any")

usual calling like foo(10,20) or foo('a',10) working perfectly. But I
have a problem with call with VARIADIC keyword

like foo(VARIADIC ARRAY[10,20]) or foo(VARIADIC ARRAY['a','10']).

Keyword VARIADIC is allowed, and this a calling doesn't raise any
error. But there isn't transformation to standard parameters. It's in
negation to other than "any" types. And because parser doesn't expand
array to parameters and just ignore VARIADIC keyword I am must not fix
it inside custom function.

so:

   FUNCTION foo(VARIADIC text[])
            -------- CALL foo(10,20,20) ---> real call
foo(ARRAY['10','20','20']);
            -------- CALL foo (VARIADIC ARRAY['10','20','20']) --->
real call foo(ARRAY['10','20','20'])

-- same mechanism should be for "any" type - in reverse order

FUNCTION foo(VARIADIC "any")
             -------- CALL foo(10,20,20)  ---> real call foo(10,20,20);
             -------- CALL foo(VARIADIC ARRAY[10,20,20]) ---> real
call foo(10,20,20) -- but it doesn't work now.

Pavel



>
> =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=
=A0 =C2=A0regards, tom lane
>

Pavel Stehule <pavel.stehule@gmail.com> writes:
> I didn't explain it well, sorry

> so I have a function foo(variadic "any")

> usual calling like foo(10,20) or foo('a',10) working perfectly. But I
> have a problem with call with VARIADIC keyword

> like foo(VARIADIC ARRAY[10,20]) or foo(VARIADIC ARRAY['a','10']).

> Keyword VARIADIC is allowed, and this a calling doesn't raise any
> error.

What exactly is the use-case for that?  You can't expect that an array
will hold the parameter list, since the parameters might not be all the
same type.

>              -------- CALL foo(VARIADIC ARRAY[10,20,20]) ---> real
> call foo(10,20,20) -- but it doesn't work now.

I'm not convinced it should work that way.  Even if you had convinced me
that this was sensible and had a real use-case, making it work like that
would take a whole bunch of mechanism that doesn't exist.

            regards, tom lane

2010/12/9 Tom Lane <tgl@sss.pgh.pa.us>:
> Pavel Stehule <pavel.stehule@gmail.com> writes:
>> I didn't explain it well, sorry
>
>> so I have a function foo(variadic "any")
>
>> usual calling like foo(10,20) or foo('a',10) working perfectly. But I
>> have a problem with call with VARIADIC keyword
>
>> like foo(VARIADIC ARRAY[10,20]) or foo(VARIADIC ARRAY['a','10']).
>
>> Keyword VARIADIC is allowed, and this a calling doesn't raise any
>> error.
>
> What exactly is the use-case for that?  You can't expect that an array
> will hold the parameter list, since the parameters might not be all the
> same type.
>

I am working on function that can help with record updating. It's
based on polymorphic types. I would to allow a multiple modification
per one call - like UPDATE statement does.

some like:

record_set_fields(anyelement, key text, value "any" [, key text, value
"any" [..]]) returns anyelement

because we cannot work with pairs of params I designed interface

CREATE FUNCTION record_set_fields(anyelement, VARIADIC "any") RETURNS anyelement

most often case working well:

SELECT record_set_fields(row(0,0,0,0,0,0), 'f1', 10, 'f2', 20, 'f3', 30)

I prefer "any" type because a user must not use a quotes for values -
and I am able to do late conversion based on record tuple desc. But
sometimes can be interesting to use a VARIADIC value - so list of
pairs (key,  value) can be created dynamically - (now I don't talk if
this is good way or not). And because we have a VARIADIC value for
VARIADIC parameter, it should be no problem - It works for non "any"
types now.

I would to do some like:

DECLARE change_set text[];
BEGIN
   change_set = ARRAY(SELECT CASE WHEN i % 2 = 1 THEN 'f' || (i / 2)
ELSE (-100)::text END FROM generate_series(1,10) g(i));
   -- change_set = {f0,-100,f1,-100,f2,-100,f3,-100,f4,-100}
  NEW := record_set_fields(NEW, VARIADIC change_set);
 ...

 RETURN NEW;

but  NEW := record_set_fields(NEW, VARIADIC change_set) doesn't work
now - because keyword VARIADIC hasn't necessary effect for "any" type.
It's just quietly ignored. Isn't a problem to expand array inside
custom function - but I don't have a info if VARIADIC keyword was used
or not.

From some custom function's perspective there isn't difference between
(when "any" type is used):

SELECT foo(VARIADIC arrayval) and SELECT foo(arrayval).

I don't know when I have to raise exception and when I have to expand array.

Regards

Pavel

p.s. I found a workaroud - but it's a workaround and needs twice code.
I have to define second record_set_fields(anyelement, VARIADIC
anyarray), and this variant is chosen when VARIADIC value is used. But
I afraid about stability of this solution.




>>              -------- CALL foo(VARIADIC ARRAY[10,20,20]) ---> real
>> call foo(10,20,20) -- but it doesn't work now.
>
> I'm not convinced it should work that way.  Even if you had convinced me
> that this was sensible and had a real use-case, making it work like that
> would take a whole bunch of mechanism that doesn't exist.
>
>                        regards, tom lane
>

Pavel Stehule <pavel.stehule@gmail.com> writes:
> 2010/12/9 Tom Lane <tgl@sss.pgh.pa.us>:
>> What exactly is the use-case for that?

> I am working on function that can help with record updating. It's
> based on polymorphic types. I would to allow a multiple modification
> per one call - like UPDATE statement does.
> some like:
> record_set_fields(anyelement, key text, value "any" [, key text, value
> "any" [..]]) returns anyelement

OK, makes sense, since you don't want to constrain the values to be all
the same datatype.

> sometimes can be interesting to use a VARIADIC value - so list of
> pairs (key,  value) can be created dynamically - (now I don't talk if
> this is good way or not).

That can't work unless you constrain all the values to be text (to match
the column-name parameters), which more or less defeats the entire point
of the function.  So I see no interesting use-case for VARIADIC here.

            regards, tom lane

2010/12/10 Tom Lane <tgl@sss.pgh.pa.us>:
> Pavel Stehule <pavel.stehule@gmail.com> writes:
>> 2010/12/9 Tom Lane <tgl@sss.pgh.pa.us>:
>>> What exactly is the use-case for that?
>
>> I am working on function that can help with record updating. It's
>> based on polymorphic types. I would to allow a multiple modification
>> per one call - like UPDATE statement does.
>> some like:
>> record_set_fields(anyelement, key text, value "any" [, key text, value
>> "any" [..]]) returns anyelement
>
> OK, makes sense, since you don't want to constrain the values to be all
> the same datatype.

ok, can I send a patch?

Pavel

>
>> sometimes can be interesting to use a VARIADIC value - so list of
>> pairs (key, =C2=A0value) can be created dynamically - (now I don't talk =
if
>> this is good way or not).
>
> That can't work unless you constrain all the values to be text (to match
> the column-name parameters), which more or less defeats the entire point
> of the function. =C2=A0So I see no interesting use-case for VARIADIC here.
>
> =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=
=A0 =C2=A0regards, tom lane
>

On Fri, Dec 10, 2010 at 2:44 PM, Pavel Stehule <pavel.stehule@gmail.com> wrote:
> 2010/12/10 Tom Lane <tgl@sss.pgh.pa.us>:
>> Pavel Stehule <pavel.stehule@gmail.com> writes:
>>> 2010/12/9 Tom Lane <tgl@sss.pgh.pa.us>:
>>>> What exactly is the use-case for that?
>>
>>> I am working on function that can help with record updating. It's
>>> based on polymorphic types. I would to allow a multiple modification
>>> per one call - like UPDATE statement does.
>>> some like:
>>> record_set_fields(anyelement, key text, value "any" [, key text, value
>>> "any" [..]]) returns anyelement
>>
>> OK, makes sense, since you don't want to constrain the values to be all
>> the same datatype.
>
> ok, can I send a patch?

In the part of Tom's email you didn't quote, he wrote "this can't
work".  Did you miss that part?

--
Robert Haas
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