On 6/27/2011 5:25 PM, Mathias Gaunard wrote:
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.
As a side note, since STRIP_PARENS needs variadic macros anyway, BOOST_FOREACH could take its arguments as variadic data without needing the end-user to put parens around its first argument when an embedded comma is present. Of course this would need for Eric Niebler to change BOOST_FOREACH to support variadics when present. Nonetheless macros using variadics to identify pp-lib data types on the fly might still be useful and I have already come up with a pretty good IS_TUPLE. Whether an IS_ARRAY, IS_LIST, or IS_SEQ is posible I shall see. I will probably end up putting any additions in my VMD library for the time being and if Paul decides that he wants them for pp-lib sometime in the future they will eventually go there.