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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/assert.hpp>
- #include <boost/hana/first.hpp>
- #include <boost/hana/fold_left.hpp>
- #include <boost/hana/insert.hpp>
- #include <boost/hana/integral_constant.hpp>
- #include <boost/hana/map.hpp>
- #include <boost/hana/pair.hpp>
- #include <boost/hana/second.hpp>
- #include <boost/hana/type.hpp>
- namespace hana = boost::hana;
- int main() {
- // Given a map of (key, value) pairs, returns a map of (value, key) pairs.
- // This requires both the keys and the values to be compile-time Comparable.
- auto invert = [](auto map) {
- return hana::fold_left(map, hana::make_map(), [](auto map, auto pair) {
- return hana::insert(map, hana::make_pair(hana::second(pair), hana::first(pair)));
- });
- };
- auto m = hana::make_map(
- hana::make_pair(hana::type_c<int>, hana::int_c<1>),
- hana::make_pair(hana::type_c<float>, hana::int_c<2>),
- hana::make_pair(hana::int_c<3>, hana::type_c<void>)
- );
- BOOST_HANA_CONSTANT_CHECK(invert(m) ==
- hana::make_map(
- hana::make_pair(hana::int_c<1>, hana::type_c<int>),
- hana::make_pair(hana::int_c<2>, hana::type_c<float>),
- hana::make_pair(hana::type_c<void>, hana::int_c<3>)
- )
- );
- }
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