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b32b8144 | 1 | // Copyright Louis Dionne 2013-2017 |
7c673cae FG |
2 | // Distributed under the Boost Software License, Version 1.0. |
3 | // (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt) | |
4 | ||
5 | #include <boost/hana/assert.hpp> | |
6 | #include <boost/hana/at_key.hpp> | |
7 | #include <boost/hana/fold_left.hpp> | |
8 | #include <boost/hana/integral_constant.hpp> | |
9 | #include <boost/hana/map.hpp> | |
10 | #include <boost/hana/pair.hpp> | |
11 | #include <boost/hana/range.hpp> | |
12 | namespace hana = boost::hana; | |
13 | ||
14 | ||
15 | // | |
16 | // Make sure that http://stackoverflow.com/q/32702383/627587 works. | |
17 | // | |
18 | ||
19 | auto at = [](auto& map, auto key) -> auto& { | |
20 | return map[key]; | |
21 | }; | |
22 | ||
23 | template <typename Map, typename Keys> | |
24 | auto& traverse(Map& map, Keys const& keys){ | |
25 | return hana::fold_left(keys, map, at); | |
26 | } | |
27 | ||
28 | int main() { | |
29 | auto xs = hana::make_map(hana::make_pair(hana::int_c<0>, | |
30 | hana::make_map(hana::make_pair(hana::int_c<1>, | |
31 | hana::make_map(hana::make_pair(hana::int_c<2>, | |
32 | hana::make_map(hana::make_pair(hana::int_c<3>, 10)))))))); | |
33 | ||
34 | int& i = traverse(xs, hana::range_c<int, 0, 4>); | |
35 | BOOST_HANA_RUNTIME_CHECK(i == 10); | |
36 | i = 99; | |
37 | BOOST_HANA_RUNTIME_CHECK(traverse(xs, hana::range_c<int, 0, 4>) == 99); | |
38 | } |