RE: CPP (preprocessor) quandry

["Buddy Lott" <buddy_lott@hotmail.com>]

Does it have to work in C or just C++?

It sounds like you are trying to simulate namespaces in c or c++.


Have you you tried something like this

#define NAMESPACE struct y {
#define ENDNAMESPACE }

Then in the code you would do:

NAMESPACE(buddy)

Typedef ...

ENDNAMESPACE

This would also allow you to "customize" name spaces to the whatever the
compiler supports.

> -----Original Message-----
> From: Eljay Love-Jensen [mailto:eljay@adobe.com]
> Sent: Friday, November 22, 2002 1:06 PM
> To: Buddy Lott; gcc-help@gcc.gnu.org
> Subject: RE: CPP (preprocessor) quandry
> 
> Hi Buddy,
> 
> The macro wraps the data type in a struct, so as to reduce namespace
> pollution.
> 
> In particular, it avoids...
> typedef enum {a,b,c} EnumWhatever;
> ...such that a, b, c and EnumWhatever now reside in the global (or
> current)
> namespace.
> 
> I have found a GCC-centric solution.  But (unfortunately) the code
needs
> to
> run on other compilers.
> 
> #define $MkEnum(name$, enum$...) \
> struct name$ {\
>    typedef enum { enum$ } Type;\
>    Type m;\
>    explicit name$ (Type in) : m(in) { }\
>    operator Type () const { return m; };\
>    }
> 
> NOTE: local convention dictates that $ is used to prefix macros
(function
> macros or simple substitution), and $ suffix for the macro's
> parameters.  The $ is digestable by all the preprocessors / compilers
we
> care about.  Less chance of spurious macro vs. local identifier
collision.
> 
> Something similar to this trick was proposed / introduced by
Stroustrup in
> his C++ Programming Language (3rd and Special editions).  Not the
macro
> part, but the wrapping of a POD in a struct to have somewhat stronger
type
> safety.  Getting that stronger type safety is the ultimate purpose of
the
> macros; the macros serve to reduce repetitive typing -- and thus
reduce
> mistakes and simplify maintenance.
> 
> A better solution would be to use a language that has this facility
> native.  Stroupstrup told me (paraphrased), "No one is stopping you
from
> writing your own language."  (I think he was a little tired of hearing
a
> bazillion requests and suggestions for how to "improve" C++.)
> 
> Sincerely,
> --Eljay
> (I hate macros)
> 
> 
> At 12:43 PM 11/22/2002 -0500, Buddy Lott wrote:
> >I can't think of a way to get around this, but maybe if you explain
what
> >purpose this solves (in other wordes, why use the macro) I could
think
> >of a way to accomplish the same thing.
> >
> >One what that comes to mind:
> >
> >Typedef enum { a,b,c} EnumWhatever;
> >MkFoo(Whatever)