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

[Eduardo Habkost]

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).

-- 
Eduardo