46 lines
1.1 KiB
C++
46 lines
1.1 KiB
C++
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/*!
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@file
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Forward declares `boost::hana::zero`.
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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_FWD_ZERO_HPP
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#define BOOST_HANA_FWD_ZERO_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 `plus`.
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//! @ingroup group-Monoid
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//!
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//! @tparam M
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//! The tag (a `Monoid`) 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/zero.cpp
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#ifdef BOOST_HANA_DOXYGEN_INVOKED
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template <typename M>
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constexpr auto zero = []() -> decltype(auto) {
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return tag-dispatched;
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};
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#else
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template <typename M, typename = void>
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struct zero_impl : zero_impl<M, when<true>> { };
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template <typename M>
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struct zero_t;
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template <typename M>
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constexpr zero_t<M> zero{};
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#endif
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BOOST_HANA_NAMESPACE_END
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#endif // !BOOST_HANA_FWD_ZERO_HPP
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