63e88f80
 Hu Chunming
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/*!
@file
Forward declares `boost::hana::not_`.
Copyright Louis Dionne 2013-2022
Distributed under the Boost Software License, Version 1.0.
(See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
*/
#ifndef BOOST_HANA_FWD_NOT_HPP
#define BOOST_HANA_FWD_NOT_HPP
#include <boost/hana/config.hpp>
#include <boost/hana/core/when.hpp>
namespace boost { namespace hana {
//! Negates a `Logical`.
//! @ingroup group-Logical
//!
//! This method returns a `Logical` with the same tag, but whose
//! truth-value is negated. Specifically, `not_(x)` returns a false-valued
//! `Logical` if `x` is a true-valued `Logical`, and a true-valued one
//! otherwise.
//!
//!
//! Example
//! -------
//! @include example/not.cpp
#ifdef BOOST_HANA_DOXYGEN_INVOKED
constexpr auto not_ = [](auto&& x) -> decltype(auto) {
return tag-dispatched;
};
#else
template <typename L, typename = void>
struct not_impl : not_impl<L, when<true>> { };
struct not_t {
template <typename X>
constexpr decltype(auto) operator()(X&& x) const;
};
BOOST_HANA_INLINE_VARIABLE constexpr not_t not_{};
#endif
}} // end namespace boost::hana
#endif // !BOOST_HANA_FWD_NOT_HPP
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