Re: [PATCH v2 3/8] qnum: QNumValue type for QNum value literals

[Eduardo Habkost]

On Wed, Nov 25, 2020 at 07:40:48AM +0100, Markus Armbruster wrote:
> Eduardo Habkost <ehabkost@redhat.com> writes:
> 
> > On Tue, Nov 24, 2020 at 04:20:37PM +0100, Markus Armbruster wrote:
> >> Eduardo Habkost <ehabkost@redhat.com> writes:
> >> 
> >> > On Tue, Nov 24, 2020 at 09:49:30AM +0100, Markus Armbruster wrote:
> >> >> Eduardo Habkost <ehabkost@redhat.com> writes:
> >> >> 
> >> >> > On Mon, Nov 23, 2020 at 08:51:27AM +0100, Markus Armbruster wrote:
> >> >> >> Eduardo Habkost <ehabkost@redhat.com> writes:
> >> >> >> 
> >> >> >> > On Fri, Nov 20, 2020 at 06:29:16AM +0100, Markus Armbruster wrote:
> >> >> >> [...]
> >> >> >> >> When the structure of a data type is to be kept away from its 
> >> >> >> >> users, I
> >> >> >> >> prefer to keep it out of the public header, so the compiler 
> >> >> >> >> enforces the
> >> >> >> >> encapsulation.
> >> >> >> >
> >> >> >> > I prefer that too, except that it is impossible when users of the
> >> >> >> > API need the compiler to know the struct size.
> >> >> >> 
> >> >> >> There are cases where the structure of a data type should be
> >> >> >> encapsulated, yet its size must be made known for performance (avoid
> >> >> >> dynamic memory allocation and pointer chasing).
> >> >> >> 
> >> >> >> Need for encapsulation correlates with complex algorithms and data
> >> >> >> structures.  The cost of dynamic allocation is often in the noise 
> >> >> >> then.
> >> >> >
> >> >> > I don't know what we are talking about anymore.  None of this
> >> >> > applies to the QNum API, right?
> >> >> >
> >> >> > QNum/QNumValue are not complex data structures, and the reason we
> >> >> > need the compiler to know the size of QNumValue is not related to
> >> >> > performance at all.
> >> >> 
> >> >> We started with the question whether to make QNumValue's members
> >> >> private.  We digressed to the question when to make members private.
> >> >> So back to the original question.
> >> >> 
> >> >> > We might still want to discourage users of the QNum API from
> >> >> > accessing QNum.u/QNumValue.u directly.  Documenting the field as
> >> >> > private is a very easy way to do it.
> >> >> 
> >> >> It's a complete non-issue.  QNum has been around for years, and we
> >> >> haven't had any issues that could've been plausibly avoided by asking
> >> >> people to refrain from accessing its members.
> >> >> 
> >> >> If there was an actual need to keep the members private, I'd move the
> >> >> struct out of the header, so the compiler enforces privacy.
> >> >
> >> > Understood.  There's still a question I'd like to answer, to
> >> > decide how the API documentation should look like:
> >> >
> >> >   Is QNum.u/QNumValue.u required to be part of the API
> >> >   documentation?
> >> >
> >> > If accessing that field directly is not necessary for using the
> >> > API, I don't think it should appear in the documentation (because
> >> > it would be just noise).
> >> 
> >> The current patch's comment on QNumValue looks good to me.
> >> 
> >> Does this answer your question?
> >
> > The current patch (v3) doesn't address the question.  It doesn't
> > include documentation for the field, but doesn't hide it.
> > kernel-doc will print a warning on that case.
> 
> Do we care?

Yes.  Peter will reject pull requests if it generates kernel-doc
warnings.

> How many such warnings exist before the patch?

Zero.

> Does this series add just this one, or more?

The current series (v3) doesn't add any, because I dropped the
patch that added QObject and QNum documentation to docs/devel.  I
still want to resubmit that patch later, though.

> 
> Use your judgement, then be ready to explain it :)

OK!

-- 
Eduardo