/*!
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@file
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Forward declares `boost::hana::one`.
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@copyright Louis Dionne 2013-2017
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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_FWD_ONE_HPP
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#define BOOST_HANA_FWD_ONE_HPP
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#include <boost/hana/config.hpp>
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#include <boost/hana/core/when.hpp>
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BOOST_HANA_NAMESPACE_BEGIN
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//! Identity of the `Ring` multiplication.
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//! @ingroup group-Ring
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//!
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//! @tparam R
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//! The tag (must be a model of `Ring`) of the returned identity.
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//!
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//!
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//! Example
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//! -------
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//! @include example/one.cpp
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#ifdef BOOST_HANA_DOXYGEN_INVOKED
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template <typename R>
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constexpr auto one = []() -> decltype(auto) {
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return tag-dispatched;
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};
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#else
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template <typename R, typename = void>
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struct one_impl : one_impl<R, when<true>> { };
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template <typename R>
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struct one_t {
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constexpr decltype(auto) operator()() const;
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};
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template <typename R>
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constexpr one_t<R> one{};
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#endif
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BOOST_HANA_NAMESPACE_END
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#endif // !BOOST_HANA_FWD_ONE_HPP
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