Subject: Re: [boost] [preprocessor] Warning: Incoming
From: Mathias Gaunard (mathias.gaunard_at_[hidden])
Date: 2011-06-27 17:25:15
On 06/27/2011 10:37 PM, Edward Diener wrote:
>> May I suggest the addition of a macro that strips parentheses but only
>> if they are present?
>
> I do not think this is possible. But I am out of the loop regarding
> pp-lib additions and Paul would really know if this could be done.
Code to do this was already given on the Boost ML by Steven Watanabe:
<http://article.gmane.org/gmane.comp.lib.boost.user/61011>
I've already been using this for a year in my code, and it works fine.
There is one little caveat with the above code, it's not strictly
conforming to C99/C++0x so it doesn't work with Wave.
Replacing
(__VA_ARGS__, 2, 1)
by
(__VA_ARGS__, 2, 1, 0)
fixes the problem.
>
>> I have found this to be very useful for passing arguments that contain
>> commas easily.
>
> Can you give an example of what you are trying to do ?
Consider something like
BOOST_FOREACH(std::pair<A, B> a, mymap)
this fails because the preprocessor sees it as three arguments.
Assuming BOOST_FOREACH was using STRIP_PARENS on its arguments, you could do
BOOST_FOREACH((std::pair<A, B> a), mymap)
in the cases where it is necessary.
This is actually pretty much a requirement when you want to write macros
that take template with multiple parameters as arguments.