Mathias Gaunard <mathias.gaunard <at> ens-lyon.org> writes:
[...]
You probably need to be able to access the final tuple with the original indices though, which is a bit more involved.
[...code...]
This could make an interesting addition to Boost.Fusion.
As a simple curiosity, here's how this could be implemented with Hana: ------------------------------------------------------------------------------ #include <boost/hana/functional.hpp> #include <boost/hana/integral_constant.hpp> #include <boost/hana/range.hpp> #include <boost/hana/tuple.hpp> #include <boost/hana/type.hpp> #include <iostream> namespace hana = boost::hana; using namespace hana::literals; int main() { auto types = hana::tuple_t<short, int, short>; auto indexed_types = hana::zip( types, hana::to<hana::Tuple>(hana::range(0_c, hana::size(types))) ); auto sorted_indexed_types = hana::sort_by([](auto t, auto u) { return hana::sizeof_(t[0_c]) < hana::sizeof_(u[0_c]); }, indexed_types); auto sorted_types = hana::transform(sorted_indexed_types, hana::head); auto sorted_indices = hana::transform(sorted_indexed_types, hana::last); using tuple = decltype( hana::unpack(sorted_types, hana::template_<hana::_tuple>) )::type; tuple t; std::cout << sizeof(t[sorted_indices[0_c]]) << std::endl; std::cout << sizeof(t[sorted_indices[1_c]]) << std::endl; std::cout << sizeof(t[sorted_indices[2_c]]) << std::endl; } ------------------------------------------------------------------------------ It's essentially the same thing than with MPL/Fusion, except there's a bit more syntactic sugar because of C++14 features. Also, this example showcases how low the syntactic cost of the MPL/Fusion unification is. The only place where we need to bridge between types and values is using tuple = decltype( hana::unpack(sorted_types, hana::template_<hana::_tuple>) )::type; which is (IMO) not too cumbersome. Regards, Louis P.S.: I know the order of the arguments to sort_by is backwards. I'm working on a consistent scheme for these algorithms.