71 lines
2.4 KiB
C++
71 lines
2.4 KiB
C++
/*!
|
|
@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
|