Re: why are we not using const?

["Richard Guenther" <richard dot guenther at gmail dot com>]

On 6/29/06, Dave Korn <dave.korn@artimi.com> wrote:
> On 29 June 2006 14:55, Andrew Pinski wrote:
>
> > On Jun 29, 2006, at 9:51 AM, Dave Korn wrote:
> >
> >>    That's cheating!  You casted away const, it's a blatant aliasing
> >> violation, you deserve everything you get.
> >
> > No it is not, in fact it is legal C and there is no aliasing
> > violation as you
> > are still accessing the memory as an "int".
>
>   Sorry, 'aliasing' was the wrong choice of word.  But it's really legal to
> cast away const?  I'm boggled.  In that case it simply might as well not exist
> at all; it conveys no usable semantic information.  I would argue that const
> should be removed from the language if this is the case; if all you want is to
> document the properties of function args, it makes more sense to do it with
> macros that #define to nothing, like M$ does with 'IN', 'OUT', 'OPTIONAL' and
> so on in all their header files.

;)

It's useful for qualifiers on the actual object like

const int foo = 1;

only for pointer targets it's useless but "needed" to form &foo, which
is const int*.  And it is undefined if you try to modify foo via

int * bar = (int*)&foo;
*bar = 1;

so, it's only the CV qualifier of the object that matters, not the one
you stick to some arbitrary pointer to an object.

The solution is of course to teach the middle-end a new concept
of pointer to non-modifiable memory and do some language extension
to use it.  Maybe there even are languages that have a useful const
concept (like C++ for the this object on const methods).

Richard.