boost/hana/extend.hpp

0001 /*!
0002 @file
0003 Defines `boost::hana::extend`.
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_EXTEND_HPP
0011 #define BOOST_HANA_EXTEND_HPP
0012
0013 #include <boost/hana/fwd/extend.hpp>
0014
0015 #include <boost/hana/concept/comonad.hpp>
0016 #include <boost/hana/config.hpp>
0017 #include <boost/hana/core/dispatch.hpp>
0018 #include <boost/hana/duplicate.hpp>
0019 #include <boost/hana/transform.hpp>
0020
0021
0022 namespace boost { namespace hana {
0023     //! @cond
0024     template <typename W_, typename F>
0025     constexpr decltype(auto) extend_t::operator()(W_&& w, F&& f) const {
0026         using W = typename hana::tag_of<W_>::type;
0027         using Extend = BOOST_HANA_DISPATCH_IF(extend_impl<W>,
0028             hana::Comonad<W>::value
0029         );
0030
0031     #ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
0032         static_assert(hana::Comonad<W>::value,
0033         "hana::extend(w, f) requires 'w' to be a Comonad");
0034     #endif
0035
0036         return Extend::apply(static_cast<W_&&>(w), static_cast<F&&>(f));
0037     }
0038     //! @endcond
0039
0040     template <typename W, bool condition>
0041     struct extend_impl<W, when<condition>> : default_ {
0042         template <typename X, typename F>
0043         static constexpr decltype(auto) apply(X&& x, F&& f) {
0044             return hana::transform(hana::duplicate(static_cast<X&&>(x)),
0045                                    static_cast<F&&>(f));
0046         }
0047     };
0048 }} // end namespace boost::hana
0049
0050 #endif // !BOOST_HANA_EXTEND_HPP