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