Horton

Re: Make copyObject work in C++

Tom Lane <tgl@sss.pgh.pa.us>

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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Jelte Fennema-Nio <postgres@jeltef.nl>
Cc: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>, Thomas Munro <thomas.munro@gmail.com>
Date: 2025-12-07T19:45:07Z
Lists: pgsql-hackers

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. Fix for C++ compatibility

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

Jelte Fennema-Nio <postgres@jeltef.nl> writes:
> Calling copyObject fails in C++ with an error like in most setups:
> error: use of undeclared identifier 'typeof'; did you mean 'typeid'
> This is due to the C compiler supporting used to compile postgres
> supporting typeof, but that function actually not being present in the
> C++ compiler. This fixes that by using decltype instead of typeof when
> including the header in C++.

Hmm, this only fixes the one use-case.  Admittedly we have only one
use-case, but as soon as we have another we'll have a new problem.
How about instead modifying the macro?  Maybe something like this
in c.h (untested):

#ifdef __cplusplus
#undef typeof
#define typeof decltype
#define HAVE_TYPEOF 1
#endif

> Another approach would be to force the value of HAVE_TYPEOF to 0 if __cplusplus.

That would be sad, because we'd lose the type checking ability
of copyObject() in C++ code.

BTW, grepping finds a number of random references to __typeof__ and
__typeof, which probably ought to be updated to be just typeof.

			regards, tom lane