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- // Copyright Louis Dionne 2013-2017
- // Distributed under the Boost Software License, Version 1.0.
- // (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
- #include <boost/hana/at.hpp>
- #include <boost/hana/back.hpp>
- #include <boost/hana/core/to.hpp>
- #include <boost/hana/front.hpp>
- #include <boost/hana/functional/on.hpp>
- #include <boost/hana/integral_constant.hpp>
- #include <boost/hana/length.hpp>
- #include <boost/hana/less.hpp>
- #include <boost/hana/pair.hpp>
- #include <boost/hana/range.hpp>
- #include <boost/hana/sort.hpp>
- #include <boost/hana/transform.hpp>
- #include <boost/hana/tuple.hpp>
- #include <boost/hana/type.hpp>
- #include <boost/hana/zip.hpp>
- #include <type_traits>
- namespace hana = boost::hana;
- using namespace hana::literals;
- auto indexed_sort = [](auto list, auto predicate) {
- auto indexed_list = hana::zip(
- list,
- hana::to_tuple(hana::make_range(0_c, hana::length(list)))
- );
- auto sorted = hana::sort.by(predicate ^hana::on^ hana::front, indexed_list);
- return hana::make_pair(hana::transform(sorted, hana::front),
- hana::transform(sorted, hana::back));
- };
- int main() {
- auto types = hana::tuple_t<char[4], char[2], char[1], char[5], char[3]>;
- auto sorted = indexed_sort(types, [](auto t, auto u) {
- return hana::sizeof_(t) < hana::sizeof_(u);
- });
- using Tup = decltype(
- hana::unpack(hana::first(sorted), hana::template_<hana::tuple>)
- )::type;
- auto indices = hana::second(indexed_sort(hana::second(sorted), hana::less));
- // When accessed through the indices sequence, the tuple appears to be
- // ordered as the `types` above. However, as can be seen in the
- // static_assert below, the tuple is actually ordered differently.
- Tup tup;
- char const(&a)[4] = tup[indices[0_c]];
- char const(&b)[2] = tup[indices[1_c]];
- char const(&c)[1] = tup[indices[2_c]];
- char const(&d)[5] = tup[indices[3_c]];
- char const(&e)[3] = tup[indices[4_c]];
- static_assert(std::is_same<
- Tup,
- hana::tuple<char[1], char[2], char[3], char[4], char[5]>
- >{}, "");
- (void)a; (void)b; (void)c; (void)d; (void)e;
- }
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