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SubjectRe: C++ in kernel (was Re: exception in a device driver)
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"Anthony Barbachan" <barbacha@Hinako.AMBusiness.com> said:
> Horst von Brand <vonbrand@inf.utfsm.cl> said:
> >"Anthony Barbachan" <barbacha@Hinako.AMBusiness.com> said:

> >> I can see at least some good uses. Start by using it as a better C,
> >> strong type checking, etc. Perhaps use some of its features to get
> >> rid of fancy uses of preprocessor macros, which are usually somewhat
> >> cryptic.

> >I don't see what can be done in C++ that can't be done in GNU C (this is
> >definitely not ANSI C!) in this area.

> I haven't used any specific options for "GNU C", or at least I do not think
> I have, so I cannot say if it can give the same benefits as C++. However,
> as far as I can tell the compiler doesn't even warn about using ancient C or
> obselete syntaxs.

I refered to creative #defines and such. And re obsolete syntax, egcs is
getting pickier. You can always increase the warning level...


[....]
> If the kernel were to use some C++, it doesn't mean that everything would
> have to be implemented in classes. I have many times written C++ programs
> which were coded completely C-like as far as my code went, but used objects
> that took care of much of the lower level grunt work or that kept things,
> like variables and functions, nicely organized and kept stupid mistakes from
> happening such as passing the wrong pointer to a function. Everything in
> the kernel would not have to be in C++ to take advantage of the language,
> however, those parts that can be best expressed in a class form could
> benefit.

Doing this _right_ would mean to redesign/rewrite the whole kernel from the
ground up. To patch C++ into it just won't cut it, IMO. BTW, C++ and C are
starting to diverge seriously, if I'm not very mistaken from cursory looks
at discussions on C9x and the C++ standard, so to get it to compile as GNU
C or as GNU C++ will get increasingly dificult. And mixed stuff is just an
accident waiting to happen.

[...]

> >That these other things you ask for don't exist as separate entities is
> >because (a) it is harder to write and maintain 3 different memory managers,
> >for instance. Heck, even _one_ gives the head hackers headache!, (b) it is

> Actually I didn't ask for this, I stated that it would be easier to be able
> to provide something such as that with classes.

The things where this is useful (filesystems and VFS, all sorts of device
drivers) have been taken care of, and the result works fine so far.

[...]

> >The first rule of good design is that it is the one from which nothing can
> >be taken away, not the one to which nothing could be added. Look at some
> >of the competition, they traded a few % here for a nice feature there, and
> >another % there for this nifty addition, and now they are a unholy mess.

> Quite true, but keep in mind that an "unholy mess" can also arise when the
> code base of a project becomes an uncomprehencable jumble of functions,
> variables, pointers, etc. I recently had to reconstruct a program who's
> code base had reached this state and it was definately not fun. Now
> obviously by using C this doesn't mean that Linux will approach this state
> but by its very nature C++ helps keep things much better catgorized and
> organized than C can.

C++ _can_ (in the hands of capable designers and programmers) help in this
way. So can C, perhaps with somewhat harder work. Both have the possibility
of creating an unholy mess. Perhaps C++ more than C as things stand today
(shifting standard, incomplete adherence to whatever standards exist, much
less experience working around the language's limitations).

[...]

> >language is _hugely_ complex, hard to get right for compilers and

> True, but most of the complexity actually comes from the addon libraries so
> much of this complexity could be avoided, especially if we stay far away
> from extensive templates, new-style casts, and exceptions (basically the
> rediculasly most complex new standard).

All this is what makes C++ useful: Just as C, C++ is mostly libraries. And
the "ridiculously most complex new standard" has been created exactly for
the sake of really enabling OO design in C++, and making the language safer
(for me, the jury is still out on these...). So if you don't use them, you
can stay with C and don't feel much difference.
--
Horst von Brand vonbrand@sleipnir.valparaiso.cl
Casilla 9G, Viña del Mar, Chile +56 32 672616

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