63 lines
1.8 KiB
C++
63 lines
1.8 KiB
C++
/*!
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@file
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Defines `boost::hana::flatten`.
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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_FLATTEN_HPP
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#define BOOST_HANA_FLATTEN_HPP
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#include <boost/hana/fwd/flatten.hpp>
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#include <boost/hana/concept/monad.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/detail/unpack_flatten.hpp>
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#include <boost/hana/functional/id.hpp>
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#include <boost/hana/fwd/chain.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>
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constexpr auto flatten_t::operator()(Xs&& xs) const {
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using M = typename hana::tag_of<Xs>::type;
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using Flatten = BOOST_HANA_DISPATCH_IF(flatten_impl<M>,
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hana::Monad<M>::value
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);
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#ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
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static_assert(hana::Monad<M>::value,
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"hana::flatten(xs) requires 'xs' to be a Monad");
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#endif
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return Flatten::apply(static_cast<Xs&&>(xs));
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}
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//! @endcond
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template <typename M, bool condition>
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struct flatten_impl<M, when<condition>> : default_ {
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template <typename Xs>
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static constexpr auto apply(Xs&& xs)
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{ return hana::chain(static_cast<Xs&&>(xs), hana::id); }
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};
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template <typename S>
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struct flatten_impl<S, when<Sequence<S>::value>> {
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template <typename Xs>
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static constexpr auto apply(Xs&& xs) {
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return detail::unpack_flatten(static_cast<Xs&&>(xs), hana::make<S>);
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}
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};
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BOOST_HANA_NAMESPACE_END
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#endif // !BOOST_HANA_FLATTEN_HPP
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