48 lines
1.2 KiB
C++
48 lines
1.2 KiB
C++
/*!
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@file
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Forward declares `boost::hana::not_`.
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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_NOT_HPP
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#define BOOST_HANA_FWD_NOT_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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//! Negates a `Logical`.
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//! @ingroup group-Logical
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//!
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//! This method returns a `Logical` with the same tag, but whose
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//! truth-value is negated. Specifically, `not_(x)` returns a false-valued
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//! `Logical` if `x` is a true-valued `Logical`, and a true-valued one
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//! otherwise.
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//!
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//!
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//! Example
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//! -------
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//! @include example/not.cpp
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#ifdef BOOST_HANA_DOXYGEN_INVOKED
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constexpr auto not_ = [](auto&& x) -> decltype(auto) {
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return tag-dispatched;
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};
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#else
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template <typename L, typename = void>
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struct not_impl : not_impl<L, when<true>> { };
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struct not_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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constexpr not_t not_{};
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#endif
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BOOST_HANA_NAMESPACE_END
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#endif // !BOOST_HANA_FWD_NOT_HPP
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