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/*!
@file
Defines `boost::hana::detail::unpack_flatten`.
@copyright Louis Dionne 2013-2016
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_DETAIL_UNPACK_FLATTEN_HPP
#define BOOST_HANA_DETAIL_UNPACK_FLATTEN_HPP
#include <boost/hana/at.hpp>
#include <boost/hana/config.hpp>
#include <boost/hana/detail/algorithm.hpp>
#include <boost/hana/detail/array.hpp>
#include <boost/hana/length.hpp>
#include <boost/hana/unpack.hpp>
#include <cstddef>
#include <utility>
BOOST_HANA_NAMESPACE_BEGIN namespace detail {
template <std::size_t ...Lengths>
struct flatten_indices {
// avoid empty arrays by appending 0 to `lengths`
static constexpr std::size_t lengths[] = {Lengths..., 0};
static constexpr auto flat_length =
detail::accumulate(lengths, lengths + sizeof...(Lengths), 0);
template <bool Inner>
static constexpr auto compute() {
detail::array<std::size_t, flat_length> indices{};
for (std::size_t index = 0, i = 0; i < sizeof...(Lengths); ++i)
for (std::size_t j = 0; j < lengths[i]; ++j, ++index)
indices[index] = (Inner ? i : j);
return indices;
}
static constexpr auto inner = compute<true>();
static constexpr auto outer = compute<false>();
template <typename Xs, typename F, std::size_t ...i>
static constexpr decltype(auto)
apply(Xs&& xs, F&& f, std::index_sequence<i...>) {
return static_cast<F&&>(f)(
hana::at_c<outer[i]>(hana::at_c<inner[i]>(
static_cast<Xs&&>(xs)
))...
);
}
};
struct make_flatten_indices {
template <typename ...Xs>
auto operator()(Xs const& ...xs) const -> detail::flatten_indices<
decltype(hana::length(xs))::value...
>;
};
template <typename Xs, typename F>
constexpr decltype(auto) unpack_flatten(Xs&& xs, F&& f) {
using Indices = decltype(hana::unpack(xs, make_flatten_indices{}));
return Indices::apply(static_cast<Xs&&>(xs), static_cast<F&&>(f),
std::make_index_sequence<Indices::flat_length>{});
}
} BOOST_HANA_NAMESPACE_END
#endif // !BOOST_HANA_DETAIL_UNPACK_FLATTEN_HPP
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