39 lines
1.2 KiB
C++
39 lines
1.2 KiB
C++
// Copyright Louis Dionne 2013-2017
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// Distributed under the Boost Software License, Version 1.0.
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// (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
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#include <boost/hana/assert.hpp>
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#include <boost/hana/at_key.hpp>
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#include <boost/hana/fold_left.hpp>
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#include <boost/hana/integral_constant.hpp>
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#include <boost/hana/map.hpp>
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#include <boost/hana/pair.hpp>
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#include <boost/hana/range.hpp>
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namespace hana = boost::hana;
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//
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// Make sure that http://stackoverflow.com/q/32702383/627587 works.
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//
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auto at = [](auto& map, auto key) -> auto& {
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return map[key];
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};
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template <typename Map, typename Keys>
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auto& traverse(Map& map, Keys const& keys){
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return hana::fold_left(keys, map, at);
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}
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int main() {
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auto xs = hana::make_map(hana::make_pair(hana::int_c<0>,
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hana::make_map(hana::make_pair(hana::int_c<1>,
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hana::make_map(hana::make_pair(hana::int_c<2>,
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hana::make_map(hana::make_pair(hana::int_c<3>, 10))))))));
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int& i = traverse(xs, hana::range_c<int, 0, 4>);
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BOOST_HANA_RUNTIME_CHECK(i == 10);
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i = 99;
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BOOST_HANA_RUNTIME_CHECK(traverse(xs, hana::range_c<int, 0, 4>) == 99);
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}
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