1 /*!
2 @file
3 Forward declares `boost::hana::negate`.
4 
5 @copyright Louis Dionne 2013-2017
6 Distributed under the Boost Software License, Version 1.0.
7 (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
8  */
9 
10 #ifndef BOOST_HANA_FWD_NEGATE_HPP
11 #define BOOST_HANA_FWD_NEGATE_HPP
12 
13 #include <boost/hana/config.hpp>
14 #include <boost/hana/core/when.hpp>
15 
16 
17 namespace boost { namespace hana {
18     //! Return the inverse of an element of a group.
19     //! @ingroup group-Group
20     //!
21     //!
22     //! Example
23     //! -------
24     //! @include example/negate.cpp
25 #ifdef BOOST_HANA_DOXYGEN_INVOKED
26     constexpr auto negate = [](auto&& x) -> decltype(auto) {
27         return tag-dispatched;
28     };
29 #else
30     template <typename G, typename = void>
31     struct negate_impl : negate_impl<G, when<true>> { };
32 
33     struct negate_t {
34         template <typename X>
35         constexpr decltype(auto) operator()(X&& x) const;
36     };
37 
38     BOOST_HANA_INLINE_VARIABLE constexpr negate_t negate{};
39 #endif
40 }} // end namespace boost::hana
41 
42 #endif // !BOOST_HANA_FWD_NEGATE_HPP
43