Re: [Boost-users] [preprocessor] removing parentheses

Subject: Re: [Boost-users] [preprocessor] removing parentheses
From: Edward Diener (eldiener_at_[hidden])
Date: 2010-08-04 17:38:28

On 8/4/2010 5:09 PM, Daniel Bradburn wrote:
> I'm not sure without seeing exactly what you are trying to do, but perhaps
>
> http://www.boost.org/doc/libs/1_43_0/libs/preprocessor/doc/ref/tuple_rem.html
>
> or
>
> http://www.boost.org/doc/libs/1_43_0/libs/preprocessor/doc/ref/tuple_rem_ctor.html
>
> Could help you.

Except that:

1) I do not know ( or normally care ) how many commas are in the 
parenthesized value ( ie. size of the tuple )

2) The value can be passed without any parentheses and therefore not be 
a tuple. For this second problem I can force the end-user always to put 
parentheses around the passed value, even if it does not need it to form 
a single macro value. But 1) would still remain a problem. Of course I 
could solve 1) by forcing the end-user to also pass the number of commas 
in the parenthesized value as a separate template parameter, but I think 
that is too much of a burden for the end-user.

I just want the end-user to pass the value as a single macro parameter, 
and to use the value without the outer parentheses if the value contains 
commas. But perhaps this is just impossible to do with C++'s macro 
facilities. The preprocessing library is so great I was hoping it could 
even solve this problem. In reality I may not need to strip off the 
parentheses from the value ( which in my particular case forms part of a 
C++ declaration ), since redundant parentheses almost ( possibly ) never 
causes a syntax error in C++.

It does seems as if the preprocessor library should have the 
functionality I require since it is able to extract a value from a 
sequence via BOOST_PP_SEQ_ELEM, and a sequence can be in the simple form 
of '(value)'. However my tests show that if I pass a non-sequence, such 
as just 'value' to BOOST_PP_SEQ_ELEM, the compiler gives a warning and 
the result is bogus.

>
>  > To: boost-users_at_[hidden]
>  > From: eldiener_at_[hidden]
>  > Date: Wed, 4 Aug 2010 16:05:57 -0400
>  > Subject: [Boost-users] [preprocessor] removing parentheses
>  >
>  > I have a single macro parameter which allows its passed value to contain
>  > commas. Therefore the user of the macro needs parentheses around the
>  > parameter if it contains one or more commas ( to does not have to ).
>  > When processing this parameter in a macro I would like to remove the
>  > outer parentheses if they are there before passing the value on for
>  > further processing. Is there a way to do this using some preprocessor
>  > library macro ?
>  >
>  > _______________________________________________
>  > Boost-users mailing list
>  > Boost-users_at_[hidden]
>  > http://lists.boost.org/mailman/listinfo.cgi/boost-users
>
>
>
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