1 /*! 2 @file 3 Forward declares `boost::hana::or_`. 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_OR_HPP 11 #define BOOST_HANA_FWD_OR_HPP 12 13 #include <boost/hana/config.hpp> 14 #include <boost/hana/core/when.hpp> 15 16 17 BOOST_HANA_NAMESPACE_BEGIN 18 //! Return whether any of the arguments is true-valued. 19 //! @ingroup group-Logical 20 //! 21 //! `or_` can be called with one argument or more. When called with 22 //! two arguments, `or_` uses tag-dispatching to find the right 23 //! implementation. Otherwise, 24 //! @code 25 //! or_(x) == x 26 //! or_(x, y, ...z) == or_(or_(x, y), z...) 27 //! @endcode 28 //! 29 //! 30 //! Example 31 //! ------- 32 //! @include example/or.cpp 33 #ifdef BOOST_HANA_DOXYGEN_INVOKED 34 constexpr auto or_ = [](auto&& x, auto&& ...y) -> decltype(auto) { 35 return tag-dispatched; 36 }; 37 #else 38 template <typename L, typename = void> 39 struct or_impl : or_impl<L, when<true>> { }; 40 41 struct or_t { 42 template <typename X, typename Y> 43 constexpr decltype(auto) operator()(X&& x, Y&& y) const; 44 45 template <typename X, typename ...Y> 46 constexpr decltype(auto) operator()(X&& x, Y&& ...y) const; 47 }; 48 49 constexpr or_t or_{}; 50 #endif 51 BOOST_HANA_NAMESPACE_END 52 53 #endif // !BOOST_HANA_FWD_OR_HPP 54