Re: Make COPY format extendable: Extract COPY TO format implementations

On Wed, Jan 10, 2024 at 3:40 PM Sutou Kouhei <kou@clear-code.com> wrote:
>
> Hi,
>
> In <CAD21AoC_dhfS97DKwTL+2nvgBOYrmN9XVYrE8w2SuDgghb-yzg@mail.gmail.com>
>   "Re: Make COPY format extendable: Extract COPY TO format implementations" on Wed, 10 Jan 2024 15:33:22 +0900,
>   Masahiko Sawada <sawada.mshk@gmail.com> wrote:
>
> >> We can use the satic const struct approach by choosing one
> >> of the followings:
> >>
> >> ...
> >>
> >> 4. ... other idea?
> >
> > It's a just idea but the fourth idea is to provide a convenient macro
> > to make it easy to construct the CopyFormatRoutine. For example,
> >
> > #define COPYTO_ROUTINE(...) (Node *) &(CopyToFormatRoutine) {__VA_ARGS__}
> >
> > static const CopyFormatRoutine testfmt_copyto_handler = {
> >     .type = T_CopyFormatRoutine,
> >     .is_from = true,
> >     .routine = COPYTO_ROUTINE (
> >         .start_fn = testfmt_copyto_start,
> >         .onerow_fn = testfmt_copyto_onerow,
> >         .end_fn = testfmt_copyto_end
> >         )
> > };
> >
> > Datum
> > copy_testfmt_handler(PG_FUNCTION_ARGS)
> > {
> >     PG_RETURN_POINTER(& testfmt_copyto_handler);
> > }
>
> Interesting. But I feel that it introduces another (a bit)
> tricky mechanism...

Right. On the other hand, I don't think the idea 3 is good for the
same reason Michael-san pointed out before[1][2].

>
> BTW, we also need to set .type:
>
>      .routine = COPYTO_ROUTINE (
>          .type = T_CopyToFormatRoutine,
>          .start_fn = testfmt_copyto_start,
>          .onerow_fn = testfmt_copyto_onerow,
>          .end_fn = testfmt_copyto_end
>          )

I think it's fine as the same is true for table AM.

[1] https://www.postgresql.org/message-id/ZXEUIy6wl4jHy6Nm%40paquier.xyz
[2] https://www.postgresql.org/message-id/ZXKm9tmnSPIVrqZz%40paquier.xyz

Regards,

--
Masahiko Sawada
Amazon Web Services: https://aws.amazon.com