Thread

Re: Don't cast away const where possible

Chao Li <li.evan.chao@gmail.com> — 2025-12-29T09:28:06Z

> On Dec 29, 2025, at 17:01, Bertrand Drouvot <bertranddrouvot.pg@gmail.com> wrote:
> 
> Hi,
> 
> On Mon, Dec 22, 2025 at 12:53:03PM +0100, Peter Eisentraut wrote:
>> On 18.12.25 14:55, Bertrand Drouvot wrote:
>>> Some functions are casting away the const qualifiers from their signatures in
>>> local variables.
>> 
>> @@ -1304,8 +1304,8 @@ merge_overlapping_ranges(FmgrInfo *cmp, Oid colloid,
>> static int
>> compare_distances(const void *a, const void *b)
>> {
>> -       DistanceValue *da = (DistanceValue *) a;
>> -       DistanceValue *db = (DistanceValue *) b;
>> +       const DistanceValue *da = (const DistanceValue *) a;
>> +       const DistanceValue *db = (const DistanceValue *) b;
>> 
>> I wonder if the better fix here wouldn't be to get rid of the cast. It's not
>> necessary, and without it the compiler would automatically warn about
>> qualifier mismatches.
> 
> Yeah, that looks better as it provides an extra safety check should the function
> signature change.
> 
>> These comparison functions seem to be a common
>> pattern.
> 
> Right, in the attached I applied your proposal on all those places.
> 
> Regards,
> 
> -- 
> Bertrand Drouvot
> PostgreSQL Contributors Team
> RDS Open Source Databases
> Amazon Web Services: https://aws.amazon.com
> <v2-0001-Don-t-cast-away-const-where-possible.patch><v2-0002-Add-const-to-read-only-TableInfo-pointers-in-pg_d.patch><v2-0003-Separate-read-and-write-pointers-in-pg_saslprep.patch>


I have similar patch at https://docs.qq.com/sheet/DR0JRQ3lPVGtCWW5q?tab=000001&_t=1761030496005&nlc=1 doing the exact same thing in pg_dump_sort.c.

Best regards,
--
Chao Li (Evan)
HighGo Software Co., Ltd.
https://www.highgo.com/