I'm trying to use the 3-argument version of the mpl::at metafunction, as described in the on-line manual[1], but I'm getting a compile error (using gcc 4.0.2): --- error: wrong number of template arguments (3, should be 2) /usr/include/boost/mpl/at_fwd.hpp:20: error: provided for 'template struct boost::mpl::at' --- Looking at at.hpp, at_fwd.hpp, and aux_/at_fwd.hpp, I don't see any sign of a 3-argument version of at; everything seems to be defined in terms of a 2-argument template. Am I doing something wrong, or is this a bug? [1] http://www.boost.org/libs/mpl/doc/refmanual/at.html