| 1 | // Copyright Louis Dionne 2013-2022 |
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| 2 | // Distributed under the Boost Software License, Version 1.0. |
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| 3 | // (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt) |
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| 4 | |
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| 5 | #include <boost/hana/at.hpp> |
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| 6 | #include <boost/hana/back.hpp> |
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| 7 | #include <boost/hana/core/to.hpp> |
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| 8 | #include <boost/hana/front.hpp> |
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| 9 | #include <boost/hana/functional/on.hpp> |
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| 10 | #include <boost/hana/integral_constant.hpp> |
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| 11 | #include <boost/hana/length.hpp> |
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| 12 | #include <boost/hana/less.hpp> |
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| 13 | #include <boost/hana/pair.hpp> |
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| 14 | #include <boost/hana/range.hpp> |
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| 15 | #include <boost/hana/sort.hpp> |
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| 16 | #include <boost/hana/transform.hpp> |
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| 17 | #include <boost/hana/tuple.hpp> |
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| 18 | #include <boost/hana/type.hpp> |
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| 19 | #include <boost/hana/zip.hpp> |
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| 20 | |
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| 21 | #include <type_traits> |
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| 22 | namespace hana = boost::hana; |
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| 23 | using namespace hana::literals; |
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| 24 | |
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| 25 | |
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| 26 | auto indexed_sort = [](auto list, auto predicate) { |
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| 27 | auto indexed_list = hana::zip( |
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| 28 | list, |
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| 29 | hana::to_tuple(hana::make_range(0_c, hana::length(list))) |
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| 30 | ); |
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| 31 | auto sorted = hana::sort.by(predicate ^hana::on^ hana::front, indexed_list); |
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| 32 | return hana::make_pair(hana::transform(sorted, hana::front), |
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| 33 | hana::transform(sorted, hana::back)); |
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| 34 | }; |
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| 35 | |
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| 36 | int main() { |
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| 37 | auto types = hana::tuple_t<char[4], char[2], char[1], char[5], char[3]>; |
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| 38 | auto sorted = indexed_sort(types, [](auto t, auto u) { |
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| 39 | return hana::sizeof_(t) < hana::sizeof_(u); |
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| 40 | }); |
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| 41 | using Tup = decltype( |
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| 42 | hana::unpack(hana::first(sorted), hana::template_<hana::tuple>) |
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| 43 | )::type; |
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| 44 | auto indices = hana::second(indexed_sort(hana::second(sorted), hana::less)); |
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| 45 | |
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| 46 | // When accessed through the indices sequence, the tuple appears to be |
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| 47 | // ordered as the `types` above. However, as can be seen in the |
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| 48 | // static_assert below, the tuple is actually ordered differently. |
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| 49 | Tup tup; |
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| 50 | char const(&a)[4] = tup[indices[0_c]]; |
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| 51 | char const(&b)[2] = tup[indices[1_c]]; |
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| 52 | char const(&c)[1] = tup[indices[2_c]]; |
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| 53 | char const(&d)[5] = tup[indices[3_c]]; |
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| 54 | char const(&e)[3] = tup[indices[4_c]]; |
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| 55 | |
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| 56 | static_assert(std::is_same< |
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| 57 | Tup, |
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| 58 | hana::tuple<char[1], char[2], char[3], char[4], char[5]> |
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| 59 | >{}, "" ); |
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| 60 | |
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| 61 | (void)a; (void)b; (void)c; (void)d; (void)e; |
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| 62 | } |
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| 63 | |
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