Re: [Boost-users] [variant] 'which' out of range assertion

Although it affects the variadic form of the mpl containers, the limit for variant types is set from the BOOST_MPL_LIMIT_LIST_SIZE macro.

Take a look at this thread: http://lists.boost.org/boost-users/2008/05/36488.php So, despite the workaround you found, it seems to be a bug.