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