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Message-ID: <1bec56e5-aef9-4d3b-b4ee-723c6575a44e@eisentraut.org>
Date: Mon, 8 Dec 2025 08:57:17 +0100
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Subject: Re: Make copyObject work in C++
To: Jelte Fennema-Nio <postgres@jeltef.nl>,
 PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>,
 Thomas Munro <thomas.munro@gmail.com>
References: 
 <CAGECzQR21OnnKiZO_1rLWO0-16kg1JBxnVq-wymYW0-_1cUNtg@mail.gmail.com>
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From: Peter Eisentraut <peter@eisentraut.org>
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 <CAGECzQR21OnnKiZO_1rLWO0-16kg1JBxnVq-wymYW0-_1cUNtg@mail.gmail.com>
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On 05.12.25 15:46, Jelte Fennema-Nio wrote:
> 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++.
> 
> Realized because of Thomas' not about how much of our headers should
> work in C++, and remembering I hit this specific problem myself.
> 
> Another approach would be to force the value of HAVE_TYPEOF to 0 if __cplusplus.

In the long run, I would like to change copyObject() to use 
typeof_unqual instead, because that handles qualifiers more correctly. 
(Currently, copyObject() of a const-qualified pointer results in a 
const-qualified pointer, which is nonsensical because the reason you 
made the copy is that you can modify it.)  See attached patch for an 
example.  Does C++ have something that is semantically similar to that?
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