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/*!
@file
Defines `boost::hana::partition`.
@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_PARTITION_HPP
#define BOOST_HANA_PARTITION_HPP
#include <boost/hana/fwd/partition.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/algorithm.hpp>
#include <boost/hana/detail/array.hpp>
#include <boost/hana/detail/decay.hpp>
#include <boost/hana/detail/nested_by.hpp> // required by fwd decl
#include <boost/hana/pair.hpp>
#include <boost/hana/unpack.hpp>
#include <cstddef>
#include <utility>
BOOST_HANA_NAMESPACE_BEGIN
//! @cond
template <typename Xs, typename Pred>
constexpr auto partition_t::operator()(Xs&& xs, Pred&& pred) const {
using S = typename hana::tag_of<Xs>::type;
using Partition = BOOST_HANA_DISPATCH_IF(partition_impl<S>,
hana::Sequence<S>::value
);
#ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
static_assert(hana::Sequence<S>::value,
"hana::partition(xs, pred) requires 'xs' to be a Sequence");
#endif
return Partition::apply(static_cast<Xs&&>(xs), static_cast<Pred&&>(pred));
}
//! @endcond
namespace detail {
template <bool ...B>
struct partition_indices {
static constexpr bool results[] = {B..., false}; // avoid empty array
static constexpr std::size_t left_size =
detail::count(results, results + sizeof...(B), true);
static constexpr std::size_t right_size = sizeof...(B) - left_size;
static constexpr auto compute_left() {
detail::array<std::size_t, left_size> indices{};
std::size_t* left = &indices[0];
for (std::size_t i = 0; i < sizeof...(B); ++i)
if (results[i])
*left++ = i;
return indices;
}
static constexpr auto compute_right() {
detail::array<std::size_t, right_size> indices{};
std::size_t* right = &indices[0];
for (std::size_t i = 0; i < sizeof...(B); ++i)
if (!results[i])
*right++ = i;
return indices;
}
static constexpr auto left_indices = compute_left();
static constexpr auto right_indices = compute_right();
template <typename S, typename Xs, std::size_t ...l, std::size_t ...r>
static constexpr auto apply(Xs&& xs, std::index_sequence<l...>,
std::index_sequence<r...>)
{
return hana::make<hana::pair_tag>(
hana::make<S>(hana::at_c<left_indices[l]>(static_cast<Xs&&>(xs))...),
hana::make<S>(hana::at_c<right_indices[r]>(static_cast<Xs&&>(xs))...)
);
}
};
template <typename Pred>
struct deduce_partition_indices {
template <typename ...Xs>
auto operator()(Xs&& ...xs) const -> detail::partition_indices<
static_cast<bool>(detail::decay<
decltype(std::declval<Pred>()(static_cast<Xs&&>(xs)))
>::type::value)...
> { return {}; }
};
}
template <typename S, bool condition>
struct partition_impl<S, when<condition>> : default_ {
template <typename Xs, typename Pred>
static constexpr auto apply(Xs&& xs, Pred&&) {
using Indices = decltype(hana::unpack(
static_cast<Xs&&>(xs), detail::deduce_partition_indices<Pred&&>{}
));
return Indices::template apply<S>(
static_cast<Xs&&>(xs),
std::make_index_sequence<Indices::left_size>{},
std::make_index_sequence<Indices::right_size>{}
);
}
};
BOOST_HANA_NAMESPACE_END
#endif // !BOOST_HANA_PARTITION_HPP
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