Thread: Add explicit casts in four places to simplehash.h

Hi hackers,

While working on an extension, I found that simplehash.h is missing explicit casts in four places. Without these casts, compiling code including simplehash.h yields warnings if the code is compiled with -Wc++-compat.

PostgreSQL seems to mostly prefer omitting the explicit casts, however there are many places where an explicit cast is actually used. Among many others, see e.g.

bool.c:
    state = (BoolAggState *) MemoryContextAlloc(agg_context, sizeof(BoolAggState));

domains.c:
   my_extra = (DomainIOData *) MemoryContextAlloc(mcxt, sizeof(DomainIOData));

What about, while not being strictly necessary for PostgreSQL itself, also adding such casts to simplehash.h so that it can be used in code where -Wc++-compat is enabled?

Attached is a small patch that adds the aforementioned casts.
Thanks for your consideration!

--
David Geier
(ServiceNow)

David Geier <geidav.pg@gmail.com> writes:
> What about, while not being strictly necessary for PostgreSQL itself, 
> also adding such casts to simplehash.h so that it can be used in code 
> where -Wc++-compat is enabled?

Seems reasonable, so done (I fixed one additional spot you missed).

The bigger picture here is that we do actually endeavor to keep
(most of) our headers C++ clean, but our tool cpluspluscheck misses
these problems because it doesn't try to use these macros.
I wonder whether there is a way to do better.

            regards, tom lane

On 11/3/22 15:50, Tom Lane wrote:
> Seems reasonable, so done (I fixed one additional spot you missed).
Thanks!
> The bigger picture here is that we do actually endeavor to keep
> (most of) our headers C++ clean, but our tool cpluspluscheck misses
> these problems because it doesn't try to use these macros.
> I wonder whether there is a way to do better.

What about having a custom header alongside cpluspluscheck which 
references all macros we care about?
We could start with the really big macros like the ones from 
simplehash.h and add as we go.
I could give this a try if deemed useful.

--
David Geier
(ServiceNow)

David Geier <geidav.pg@gmail.com> writes:
> On 11/3/22 15:50, Tom Lane wrote:
>> The bigger picture here is that we do actually endeavor to keep
>> (most of) our headers C++ clean, but our tool cpluspluscheck misses
>> these problems because it doesn't try to use these macros.
>> I wonder whether there is a way to do better.

> What about having a custom header alongside cpluspluscheck which 
> references all macros we care about?

Can't see that that would help, because of the hand maintenance
required to make it useful.

            regards, tom lane