48 lines
1.6 KiB
C++
48 lines
1.6 KiB
C++
/*!
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@file
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Forward declares `boost::hana::detail::nested_to`.
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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_DETAIL_NESTED_TO_FWD_HPP
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#define BOOST_HANA_DETAIL_NESTED_TO_FWD_HPP
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#include <boost/hana/config.hpp>
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namespace boost { namespace hana { namespace detail {
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template <typename Algorithm>
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struct nested_to_t {
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template <typename X>
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constexpr decltype(auto) operator()(X&& x) const;
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};
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//! @ingroup group-details
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//! Provides a `.to` static constexpr function object.
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//!
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//! When creating a binary function object of type `Algo` whose signature
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//! is `Object x Object -> Return`, `nested_to<Algo>` can be used as a base
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//! class of `Algo`. Doing so will provide a static constexpr member called
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//! `to`, which has the following signature:
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//! @code
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//! Object -> Object -> Return
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//! @endcode
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//!
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//! Note that the function object `Algo` must be default-constructible,
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//! since the algorithm will be called as `Algo{}(arguments...)`.
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//!
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//! @note
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//! This function object is especially useful because it takes care of
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//! avoiding ODR violations caused by the nested static constexpr member.
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template <typename Algorithm>
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struct nested_to { static constexpr nested_to_t<Algorithm> to{}; };
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template <typename Algorithm>
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constexpr nested_to_t<Algorithm> nested_to<Algorithm>::to;
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} }} // end namespace boost::hana
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#endif // !BOOST_HANA_DETAIL_NESTED_TO_FWD_HPP
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