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