Re: Proposal: Make use of C99 designated initialisers for nulls/values arrays

On Sat, Oct 5, 2019 at 3:10 AM Andres Freund <andres(at)anarazel(dot)de> wrote:
>
> On 2019-10-04 17:08:29 -0400, Tom Lane wrote:
> > Andres Freund <andres(at)anarazel(dot)de> writes:
> > > On 2019-10-04 16:31:29 -0400, Bruce Momjian wrote:
> > >> Yeah, it is certainly weird that you have to assign the first array
> > >> element to get the rest to be zeros. By using a macro, we can document
> > >> this behavior in one place.
> >
> > > IDK, to me this seems like something one just has to learn about C, with
> > > the macro just obfuscating that already required knowledge. It's not
> > > like this only applies to stack variables initializes with {0}. It's
> > > also true of global variables, or function-local static ones, for
> > > example.
> >
> > Huh? For both those cases, the *default* behavior, going back to K&R C,
> > is that the variable initializes to all-bits-zero. There's no need to
> > write anything extra.
>
> What I mean is that if there's any initialization, it's to all zeroes,
> except for the parts explicitly initialized explicitly. And all that the
> {0} does, is that the rest of the fields are initialized the way other
> such initialization happens.
>

You have a point and I think over time everyone will know this.
However, so many people advocating for having a macro with a comment
to be more explicit about this behavior shows that this is not equally
obvious to everyone or at least they think that it will help future
patch authors.

Now, I think as the usage ({0}) already exists in the code, so I think
if we decide to use a macro, then ideally those places should also be
changed. I am not telling that it must be done in the same patch, we
can even do it as a separate patch.

I am personally still in the camp of people advocating the use of
macro for this purpose. It is quite possible after reading your
points, some people might change their opinion or some others also
share their opinion against using a macro in which case we can drop
the idea of using a macro.

--
With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com