Re: Make copyObject work in C++

On 10.01.26 12:09, Jelte Fennema-Nio wrote:
> On Sat Jan 3, 2026 at 10:32 AM CET, Jelte Fennema-Nio wrote:
>> Attached is a patchset that does that. It required a few more fixes to
>> make the extension compile on MSVC too.
>
> Rebased after Peter merged the C++ improvements from the other thread.

I have a couple of comments on the sample extension module.

I think this module should have a runtime test, too. Otherwise you
don't know that you got the linkage correct, or whether this works at
all. It doesn't have to do much, like it could literally be a + b, and
it could evolve in the future to test hooks, _PG_init, etc.

Let's put a README file in the module's directory instead of putting the
explanation into the Makefile/meson.build.

I wonder if the module's build integration would work correctly in the
autoconf/makefile case if no C++ is available. AFAICT, it would fail to
build with g++ not found or similar.

AFAICT, the minimum changes to get a minimum test module to work are

- fix for "restrict", recently committed
- disable warning about zero-length arrays, seems trivial
- named designated initializers

I learned that named designated initializers in C++ are not allowed to
be specified out of order, so they are not a full equivalent to the C
syntax. This could be a problem for example if someone wanted in the
future to have something like

PG_MODULE_MAGIC_EXT(.threads_supported = true)

(while not specifying the leading .name and .version fields).

I think for now the easiest fix would be to just not use the named
initializers in the definition of PG_MODULE_MAGIC_DATA. Then we don't
need to require C++20 and have that additional code. In the future, we
might need a different solution more suitable for C++.

The use of -std=c++11 for CI is a valid idea; I have often wanted that
for C as well. But conversely we also want to allow testing optional
extension and future C standard features. So we need a comprehensive
solution there that covers both ends and both languages. Let's leave
that out for now and think about it separately.