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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/at_key.hpp>
- #include <boost/hana/fold_left.hpp>
- #include <boost/hana/integral_constant.hpp>
- #include <boost/hana/map.hpp>
- #include <boost/hana/pair.hpp>
- #include <boost/hana/range.hpp>
- namespace hana = boost::hana;
- //
- // Make sure that http://stackoverflow.com/q/32702383/627587 works.
- //
- auto at = [](auto& map, auto key) -> auto& {
- return map[key];
- };
- template <typename Map, typename Keys>
- auto& traverse(Map& map, Keys const& keys){
- return hana::fold_left(keys, map, at);
- }
- int main() {
- auto xs = hana::make_map(hana::make_pair(hana::int_c<0>,
- hana::make_map(hana::make_pair(hana::int_c<1>,
- hana::make_map(hana::make_pair(hana::int_c<2>,
- hana::make_map(hana::make_pair(hana::int_c<3>, 10))))))));
- int& i = traverse(xs, hana::range_c<int, 0, 4>);
- BOOST_HANA_RUNTIME_CHECK(i == 10);
- i = 99;
- BOOST_HANA_RUNTIME_CHECK(traverse(xs, hana::range_c<int, 0, 4>) == 99);
- }
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