Re: [boost] Re: new macro - BOOST_WORKAROUND(symbol, test)

From: Gennaro Prota (gennaro_prota_at_[hidden])
Date: 2002-12-08 14:22:48

--- David Abrahams <dave_at_[hidden]> wrote:
> Gennaro Prota <gennaro_prota_at_[hidden]> writes:
> 
> > On Sun, 08 Dec 2002 12:34:48 -0500, David Abrahams
> > <dave_at_[hidden]> wrote:
> >
> > [snip]
> >>> // untested
> >>> #define BOOST_PSEUDO_IS_DEFINED(symbol) BOOST_JOIN(symbol, 1)
> >>> #define BOOST_WORKAROUND(symbol, test) \
> >>>          (BOOST_PSEUDO_IS_DEFINED(symbol) && symbol test)
> >>
> >>This will fail if "symbol1" is defined, won't it?
> >
> > Oops, due to the font used when reading mails from Yahoo, I thought
> > this was a typo for "symbol" :-s Yes, you are right. It wasn't
> > intended as a solution to
> >
> >>>  b) "hides" possible problems in the (unlikely, granted) case that
> >>>      X is undefined but X1 is and you write:
> >>>
> >>>            BOOST_WORKAROUND(X, test)
> >>>
> >>>     (the result "unexpectedly" depends on the expansion of X1).
> 
> Actually, I tested my solution for that problem and it was OK. That's
> the reason I was pasting that long BOOST_NUMERIC_DEFINED_SUFFIX symbol
> to it: the idea was that probably nobody defines the
> __SUNPRO_CCBOOST_NUMERIC_DEFINED_SUFFIX symbol, for example.

Well, there's no problem with __SUNPRO_CCBOOST_NUMERIC_DEFINED_SUFFIX, just
with __SUNPRO_CC1.

> Well, then I tested your solution and it was also OK on all the
> compilers I have on my machine:
> 
>     # include <boost/config.hpp>
> 
>     #define BOOST_PSEUDO_IS_DEFINED(symbol) BOOST_JOIN(symbol, 1)
>     #define BOOST_WORKAROUND(symbol, test) \
>              (BOOST_PSEUDO_IS_DEFINED(symbol) && symbol test)
> 
>     # define SOME_COMPILER_MACRO1 0
> 
>     # if BOOST_WORKAROUND(SOME_COMPILER_MACRO, > 0)
>     #  error whoops 
>     # endif 

As I said, when SOME_COMPILER_MACRO1 is defined but SOME_COMPILER_MACRO isn't
then the result depends on the expansion of SOME_COMPILER_MACRO1 (and possibly
on the test, of course). In this case the condition of the #if becomes:

   (0 && SOME_COMPILER_MACRO > 0)

and then, of course

   (0 && 0 > 0)

Now, try defining

 #define SOME_COMPILER_MACRO1  5

and change the test e.g. to <= 1200

[...]
> BOOST_PP_CAT has several workarounds for broken compilers, and I
> wanted to get it right first before worrying about that particular
> dependency.

Yeah, I noticed that. I don't know what problems do they solve though so I'm
not sure if they are needed in the case of BOOST_WORKAROUND. Maybe they have
just to do with passing empty arguments?

Genny.

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