boost/hana/or.hpp

0001 /*!
0002 @file
0003 Defines `boost::hana::or_`.
0004
0005 Copyright Louis Dionne 2013-2022
0006 Distributed under the Boost Software License, Version 1.0.
0007 (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
0008  */
0009
0010 #ifndef BOOST_HANA_OR_HPP
0011 #define BOOST_HANA_OR_HPP
0012
0013 #include <boost/hana/fwd/or.hpp>
0014
0015 #include <boost/hana/concept/logical.hpp>
0016 #include <boost/hana/config.hpp>
0017 #include <boost/hana/core/dispatch.hpp>
0018 #include <boost/hana/detail/variadic/foldl1.hpp>
0019 #include <boost/hana/if.hpp>
0020
0021
0022 namespace boost { namespace hana {
0023     //! @cond
0024     template <typename X, typename Y>
0025     constexpr decltype(auto) or_t::operator()(X&& x, Y&& y) const {
0026         using Bool = typename hana::tag_of<X>::type;
0027         using Or = BOOST_HANA_DISPATCH_IF(or_impl<Bool>,
0028             hana::Logical<Bool>::value
0029         );
0030
0031     #ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
0032         static_assert(hana::Logical<Bool>::value,
0033         "hana::or_(x, y) requires 'x' to be a Logical");
0034     #endif
0035
0036         return Or::apply(static_cast<X&&>(x), static_cast<Y&&>(y));
0037     }
0038
0039     template <typename X, typename ...Y>
0040     constexpr decltype(auto) or_t::operator()(X&& x, Y&& ...y) const {
0041         return detail::variadic::foldl1(
0042             *this,
0043             static_cast<X&&>(x),
0044             static_cast<Y&&>(y)...
0045         );
0046     }
0047     //! @endcond
0048
0049     template <typename L, bool condition>
0050     struct or_impl<L, when<condition>> : hana::default_ {
0051         template <typename X, typename Y>
0052         static constexpr decltype(auto) apply(X&& x, Y&& y) {
0053             //! @todo How to forward `x` here? Since the arguments to `if_`
0054             //! can be evaluated in any order, we have to be careful not to
0055             //! use `x` in a moved-from state.
0056             return hana::if_(x, x, static_cast<Y&&>(y));
0057         }
0058     };
0059 }} // end namespace boost::hana
0060
0061 #endif // !BOOST_HANA_OR_HPP