54 lines
1.4 KiB
C++
54 lines
1.4 KiB
C++
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/*!
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@file
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Forward declares `boost::hana::union_`.
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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_UNION_HPP
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#define BOOST_HANA_FWD_UNION_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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//! Returns the union of two sets.
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//! @relates hana::set
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//!
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//! Given two sets `xs` and `ys`, `union_(xs, ys)` is a new set containing
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//! all the elements of `xs` and all the elements of `ys`, without
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//! duplicates. For any object `x`, the following holds:
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//! @code
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//! x ^in^ union_(xs, ys) if and only if x ^in^ xs || x ^in^ ys
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//! @endcode
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//!
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//!
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//! @param xs, ys
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//! Two sets to compute the union of.
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//!
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//!
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//! Example
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//! -------
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//! @include example/union.cpp
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#ifdef BOOST_HANA_DOXYGEN_INVOKED
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constexpr auto union_ = [](auto&& xs, auto&& ys) {
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return tag-dispatched;
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};
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#else
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template <typename S, typename = void>
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struct union_impl : union_impl<S, when<true>> { };
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struct union_t {
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template <typename Xs, typename Ys>
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constexpr auto operator()(Xs&& xs, Ys&& ys) const;
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};
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constexpr union_t union_{};
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#endif
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BOOST_HANA_NAMESPACE_END
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#endif // !BOOST_HANA_FWD_UNION_HPP
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