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

From: David Abrahams (dave_at_[hidden])
Date: 2002-12-08 13:57:24

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, 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 

    # if !BOOST_WORKAROUND(SOME_COMPILER_MACRO1, == 0)
    #  error whoops2
    # endif

    int main()
    {
        return 0;
    }

So now I guess I really don't understand the preprocessor.

> just as an (untested) way to avoid the dependency on the preprocessor
> library. It is exactly the same of the current implementation, except
> that uses BOOST_JOIN instead of BOOST_PP_CAT.

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

-- 
                       David Abrahams
   dave_at_[hidden] * http://www.boost-consulting.com
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