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/*!
@file
Defines `boost::hana::group`.
@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_GROUP_HPP
#define BOOST_HANA_GROUP_HPP
#include <boost/hana/fwd/group.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/nested_by.hpp> // required by fwd decl
#include <boost/hana/equal.hpp>
#include <boost/hana/length.hpp>
#include <cstddef>
#include <utility>
BOOST_HANA_NAMESPACE_BEGIN
//! @cond
template <typename Xs>
constexpr auto group_t::operator()(Xs&& xs) const {
using S = typename hana::tag_of<Xs>::type;
using Group = BOOST_HANA_DISPATCH_IF(group_impl<S>,
hana::Sequence<S>::value
);
#ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
static_assert(hana::Sequence<S>::value,
"hana::group(xs) requires 'xs' to be a Sequence");
#endif
return Group::apply(static_cast<Xs&&>(xs));
}
template <typename Xs, typename Predicate>
constexpr auto group_t::operator()(Xs&& xs, Predicate&& pred) const {
using S = typename hana::tag_of<Xs>::type;
using Group = BOOST_HANA_DISPATCH_IF(group_impl<S>,
hana::Sequence<S>::value
);
#ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
static_assert(hana::Sequence<S>::value,
"hana::group(xs, predicate) requires 'xs' to be a Sequence");
#endif
return Group::apply(static_cast<Xs&&>(xs),
static_cast<Predicate&&>(pred));
}
//! @endcond
namespace detail {
template <typename Xs, std::size_t ...i>
constexpr auto get_subsequence_(Xs&& xs, std::index_sequence<i...>) {
using S = typename hana::tag_of<Xs>::type;
return hana::make<S>(hana::at_c<i>(static_cast<Xs&&>(xs))...);
}
template <std::size_t offset, typename Indices>
struct offset_by;
template <std::size_t offset, std::size_t ...i>
struct offset_by<offset, std::index_sequence<i...>> {
using type = std::index_sequence<(offset + i)...>;
};
template <bool ...b>
struct group_indices {
static constexpr bool bs[] = {b...};
static constexpr std::size_t n_groups =
detail::count(bs, bs + sizeof(bs), false) + 1;
static constexpr auto compute_info() {
detail::array<std::size_t, n_groups> sizes{}, offsets{};
for (std::size_t g = 0, i = 0, offset = 0; g < n_groups; ++g) {
offsets[g] = offset;
sizes[g] = 1;
while (i < sizeof...(b) && bs[i++])
++sizes[g];
offset += sizes[g];
}
return std::make_pair(offsets, sizes);
}
static constexpr auto info = compute_info();
static constexpr auto group_offsets = info.first;
static constexpr auto group_sizes = info.second;
template <typename S, typename Xs, std::size_t ...i>
static constexpr auto finish(Xs&& xs, std::index_sequence<i...>) {
return hana::make<S>(
detail::get_subsequence_(
static_cast<Xs&&>(xs),
typename offset_by<
group_offsets[i],
std::make_index_sequence<group_sizes[i]>
>::type{}
)...
);
}
};
} // end namespace detail
template <typename S, bool condition>
struct group_impl<S, when<condition>> : default_ {
template <typename Xs, typename Pred, std::size_t ...i>
static constexpr auto
group_helper(Xs&& xs, Pred&& pred, std::index_sequence<0, i...>) {
using info = detail::group_indices<static_cast<bool>(decltype(
pred(hana::at_c<i - 1>(static_cast<Xs&&>(xs)),
hana::at_c<i>(static_cast<Xs&&>(xs)))
)::value)...>;
return info::template finish<S>(static_cast<Xs&&>(xs),
std::make_index_sequence<info::n_groups>{}
);
}
template <typename Xs, typename Pred>
static constexpr auto
group_helper(Xs&& xs, Pred&&, std::index_sequence<0>) {
return hana::make<S>(static_cast<Xs&&>(xs));
}
template <typename Xs, typename Pred>
static constexpr auto
group_helper(Xs&&, Pred&&, std::index_sequence<>) {
return hana::make<S>();
}
template <typename Xs, typename Pred>
static constexpr auto apply(Xs&& xs, Pred&& pred) {
constexpr std::size_t len = decltype(hana::length(xs))::value;
return group_helper(static_cast<Xs&&>(xs),
static_cast<Pred&&>(pred),
std::make_index_sequence<len>{});
}
template <typename Xs>
static constexpr auto apply(Xs&& xs)
{ return group_impl::apply(static_cast<Xs&&>(xs), hana::equal); }
};
BOOST_HANA_NAMESPACE_END
#endif // !BOOST_HANA_GROUP_HPP
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