On Fri, Jul 29, 2011 at 12:52 PM, Eric Niebler <eric@boostpro.com> 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.
(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.)
I'm confused. Why would fusion::detail::clear (which I presume is associated with fusion::clear) have anything to do with mpl::clear? Also, mpl::clear requires an MPL Extensible Sequence, which...I'm guessing fusion::joint_view doesn't satisfy...? So either make fusion::joint_view an MPL Extensible Sequence, or relax the requirements on mpl::clear...? I'm not sure either make sense, really. I guess there's some reason you don't want to or can't copy the types in the joint_view into an mpl::vector and operate on that instead? - Jeff