87 lines
3.0 KiB
C++
87 lines
3.0 KiB
C++
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/*!
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@file
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Defines `boost::hana::remove_at` and `boost::hana::remove_at_c`.
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@copyright Louis Dionne 2013-2016
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Distributed under the Boost Software License, Version 1.0.
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(See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
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*/
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#ifndef BOOST_HANA_REMOVE_AT_HPP
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#define BOOST_HANA_REMOVE_AT_HPP
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#include <boost/hana/fwd/remove_at.hpp>
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#include <boost/hana/at.hpp>
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#include <boost/hana/concept/integral_constant.hpp>
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#include <boost/hana/concept/sequence.hpp>
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#include <boost/hana/config.hpp>
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#include <boost/hana/core/dispatch.hpp>
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#include <boost/hana/core/make.hpp>
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#include <boost/hana/integral_constant.hpp>
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#include <boost/hana/length.hpp>
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#include <cstddef>
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#include <utility>
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BOOST_HANA_NAMESPACE_BEGIN
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//! @cond
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template <typename Xs, typename N>
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constexpr auto remove_at_t::operator()(Xs&& xs, N const& n) const {
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using S = typename hana::tag_of<Xs>::type;
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using RemoveAt = BOOST_HANA_DISPATCH_IF(remove_at_impl<S>,
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hana::Sequence<S>::value &&
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hana::IntegralConstant<N>::value
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);
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#ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
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static_assert(hana::Sequence<S>::value,
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"hana::remove_at(xs, n) requires 'xs' to be a Sequence");
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static_assert(hana::IntegralConstant<N>::value,
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"hana::remove_at(xs, n) requires 'n' to be an IntegralConstant");
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#endif
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static_assert(N::value >= 0,
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"hana::remove_at(xs, n) requires 'n' to be non-negative");
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return RemoveAt::apply(static_cast<Xs&&>(xs), n);
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}
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//! @endcond
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template <typename S, bool condition>
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struct remove_at_impl<S, when<condition>> : default_ {
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template <typename Xs, std::size_t ...before, std::size_t ...after>
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static constexpr auto
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remove_at_helper(Xs&& xs, std::index_sequence<before...>,
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std::index_sequence<after...>)
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{
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return hana::make<S>(
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hana::at_c<before>(static_cast<Xs&&>(xs))...,
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hana::at_c<after + sizeof...(before) + 1>(static_cast<Xs&&>(xs))...
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);
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}
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template <typename Xs, typename N>
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static constexpr auto apply(Xs&& xs, N const&) {
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constexpr std::size_t n = N::value;
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constexpr std::size_t len = decltype(hana::length(xs))::value;
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static_assert(n < len,
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"hana::remove_at(xs, n) requires 'n' to be in the bounds of the sequence");
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return remove_at_helper(static_cast<Xs&&>(xs),
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std::make_index_sequence<n>{},
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std::make_index_sequence<len - n - 1>{});
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}
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};
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template <std::size_t n>
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struct remove_at_c_t {
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template <typename Xs>
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constexpr decltype(auto) operator()(Xs&& xs) const
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{ return hana::remove_at(static_cast<Xs&&>(xs), hana::size_c<n>); }
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};
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BOOST_HANA_NAMESPACE_END
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#endif // !BOOST_HANA_REMOVE_AT_HPP
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