Re: [PATCH]: Fix problematic -Wcast-qual cases using new CONST_CAST macro

[Gabriel Dos Reis <gdr@cs.tamu.edu>]

"Kaveh R. GHAZI" <ghazi@caip.rutgers.edu> writes:

| On Fri, 27 Jul 2007, Kaveh R. GHAZI wrote:
| 
| > On Fri, 27 Jul 2007, Richard Guenther wrote:
| >
| > > On 7/27/07, Kaveh R. GHAZI <ghazi@caip.rutgers.edu> wrote:
| > > > Sure.  Besides my main point which is silencing -Wcast-qual warnings, the
| > > > CONST_CAST macro is grep-able.  I.e. you can search for the few places
| > > > where it's used and audit if they are correctly applied.  You cannot do
| > > > that with regular C-style casts.  Another reason is that with C-style
| > > > casts there isn't any indication of why it's there.  The CONST_CAST macro
| > > > comments itself to someone reading the code.  (These are some of the
| > > > rationales for the creation of C++'s cast operators.)  The macro isn't
| > > > type-safe like the C++ operator is, but it's a poor man's C option. :-)
| > >
| > > Ha!  Maybe a reason to switch to C++ ;)  How about
| > >
| > > #ifdef __cplusplus
| > > #define CONST_CAST(x)  .. template magic follows ..
| > > #else
| > > ...
| > > #endif
| > >
| > > ? ;)
| > > Richard.
| >
| > I don't think that will work in a generic way.  For static_cast, you need
| > to supply the stripped type like so:
| >
| > static_cast<STRIPPED-TYPE>(EXPR)
| >
| > Since we don't yet have a variant of __typeof to get the qualifer stripped
| > type for us, we'd need to pass in the stripped type to the macro like so:
| >
| > #ifdef __cplusplus
| > #define CONST_CAST(X,TYPE)  static_cast<TYPE>(X)
| >
| > Note this doesn't increase type safety for most of the cases we'll use it
| > in because we're just passing the pointer into a situation that takes a
| > void* like free(foo).  I'm not sure this change is worth it so I'd rather
| > leave this refinement to the folks who care about compiling gcc with a C++
| > compiler if they care to take this step.
| >
| > Also, I don't believe the main sources are compilable with a C++ compiler
| > at this point anyway.  Only the libiberty/ and gcc/cp/ directories use
| > -Wc++-compat AFAICT.
| >
| > So may I install the latest version of my patch?
| 
| 
| Richard, do you have any remaining objections to this patch?
| http://gcc.gnu.org/ml/gcc-patches/2007-07/msg01993.html
| 
| If there is some C++ magic you want, can you please suggest something?

Since this patch does not prepare for enabling C++ codes, I'm fine
with it as it is.  I would not suggest more __typeof magic at this
moment.  Of course, it would have been better if the codes were
written in such a way that the casts were almost never needed.

Richard G.  How strongly do you feel about this?

-- Gaby