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Re: Make copyObject work in C++

Peter Eisentraut <peter@eisentraut.org>

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From: Peter Eisentraut <peter@eisentraut.org>
To: Jelte Fennema-Nio <postgres@jeltef.nl>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>, Thomas Munro <thomas.munro@gmail.com>
Date: 2026-01-14T15:59:55Z
Lists: pgsql-hackers 
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.

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. Enable test_cplusplusext with MSVC

  2. Disable some C++ warnings in MSVC

  3. meson: Make room for C++-only warning flags for MSVC

  4. Make fixed-length list building macros work in C++

  5. Make unconstify and unvolatize use StaticAssertVariableIsOfTypeMacro

  6. Use typeof everywhere instead of compiler specific spellings

  7. Test List macros in C++ extensions

  8. Test most StaticAssert macros in C++ extensions

  9. Revert "Change copyObject() to use typeof_unqual"

  10. Fix for C++ compatibility

  11. tests: Add a test C++ extension module