114 lines
3.8 KiB
C++
114 lines
3.8 KiB
C++
/*!
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@file
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Defines `boost::hana::cartesian_product`.
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@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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*/
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#ifndef BOOST_HANA_CARTESIAN_PRODUCT_HPP
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#define BOOST_HANA_CARTESIAN_PRODUCT_HPP
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#include <boost/hana/fwd/cartesian_product.hpp>
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#include <boost/hana/at.hpp>
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#include <boost/hana/concept/sequence.hpp>
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#include <boost/hana/config.hpp>
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#include <boost/hana/core/dispatch.hpp>
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#include <boost/hana/core/make.hpp>
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#include <boost/hana/detail/array.hpp>
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#include <boost/hana/integral_constant.hpp>
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#include <boost/hana/length.hpp>
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#include <boost/hana/unpack.hpp>
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#include <cstddef>
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#include <utility>
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namespace boost { namespace hana {
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//! @cond
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template <typename Xs>
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constexpr auto cartesian_product_t::operator()(Xs&& xs) const {
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using S = typename hana::tag_of<Xs>::type;
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using CartesianProduct = BOOST_HANA_DISPATCH_IF(
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cartesian_product_impl<S>,
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hana::Sequence<S>::value
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);
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#ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
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static_assert(hana::Sequence<S>::value,
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"hana::cartesian_product(xs) requires 'xs' to be a Sequence");
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#endif
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return CartesianProduct::apply(static_cast<Xs&&>(xs));
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}
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//! @endcond
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namespace detail {
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template <std::size_t ...Lengths>
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struct cartesian_product_indices {
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static constexpr std::size_t total_length() {
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std::size_t lengths[sizeof...(Lengths)] = {Lengths...};
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std::size_t r = 1;
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for (std::size_t len: lengths)
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r *= len;
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return r;
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}
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static constexpr std::size_t length = total_length();
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static constexpr auto indices_of(std::size_t i) {
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constexpr std::size_t lengths[sizeof...(Lengths)] = {Lengths...};
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constexpr std::size_t n = sizeof...(Lengths);
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detail::array<std::size_t, n> result{};
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for (std::size_t j = n; j--;) {
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result[j] = i % lengths[j];
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i /= lengths[j];
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}
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return result;
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}
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template <typename S, std::size_t n, std::size_t ...k, typename ...Xs>
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static constexpr auto
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product_element(std::index_sequence<k...>, Xs&& ...xs) {
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constexpr auto indices = indices_of(n);
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return hana::make<S>(hana::at_c<indices[k]>(xs)...);
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}
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template <typename S, std::size_t ...n, typename ...Xs>
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static constexpr auto
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create_product(std::index_sequence<n...>, Xs&& ...xs) {
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return hana::make<S>(product_element<S, n>(
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std::make_index_sequence<sizeof...(Xs)>{}, xs...
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)...);
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}
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};
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}
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// Credits: implementation adapted from http://github.com/alexk7/hel.
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template <typename S, bool condition>
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struct cartesian_product_impl<S, when<condition>> : default_ {
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template <typename Xs>
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static constexpr auto apply(Xs&& xs) {
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return hana::unpack(static_cast<Xs&&>(xs), cartesian_product_impl{});
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}
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template <typename ...Xs>
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constexpr auto operator()(Xs&& ...xs) const {
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using indices = detail::cartesian_product_indices<
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decltype(hana::length(xs))::value...
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>;
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return indices::template create_product<S>(
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std::make_index_sequence<indices::length>{},
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static_cast<Xs&&>(xs)...);
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}
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constexpr auto operator()() const {
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return hana::make<S>();
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}
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};
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}} // end namespace boost::hana
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#endif // !BOOST_HANA_CARTESIAN_PRODUCT_HPP
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