On 7/30/2011 3:52 AM, Eric Niebler wrote:
Today I ran into a limitation in Fusion/MPL interoperability. I couldn't use an mpl algorithm on a Fusion sequence because mpl::clear wasn't defined on it. The sequence was a joint_view. I see that fusion::detail::clear is only defined for Fusion cons, map, set, vector and deque. Can we get it defined for all Fusion sequences? I think for everything else, an empty Fusion vector would do. That is all fusion::clear does, btw.
One major difference between MPL and Fusion is that operations like these in MPL preserve the original sequence type. E.g. clearing an mpl::vector will give you an empty mpl::vector. That is why it is only defined for those containers you mentioned. Clearly, clearing a joint_view will not be a sequence-type preserving operation. In the same vein all MPL 'views' cannot be cleared. Try mpl::clear on an mpl view, for example.
(Aside: it seems strange to me that mpl::clear of a fusion::set gives an empty set, but that fusion::clear of an empty set gives an empty vector. This should probably be made consistent.)
OK. It's been a while since I've touched the code. Feel free to commit a patch. It looks like bug. Regards, -- Joel de Guzman http://www.boostpro.com http://boost-spirit.com