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Diffstat (limited to '')
-rw-r--r-- | src/boost/libs/hana/example/map/foldable.cpp | 39 |
1 files changed, 39 insertions, 0 deletions
diff --git a/src/boost/libs/hana/example/map/foldable.cpp b/src/boost/libs/hana/example/map/foldable.cpp new file mode 100644 index 000000000..1884220a3 --- /dev/null +++ b/src/boost/libs/hana/example/map/foldable.cpp @@ -0,0 +1,39 @@ +// 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>) + ) + ); +} |