| 1 | /*! |
|---|---|
| 2 | @file |
| 3 | Defines `boost::hana::extract`. |
| 4 | |
| 5 | Copyright Louis Dionne 2013-2022 |
| 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_EXTRACT_HPP |
| 11 | #define BOOST_HANA_EXTRACT_HPP |
| 12 | |
| 13 | #include <boost/hana/fwd/extract.hpp> |
| 14 | |
| 15 | #include <boost/hana/concept/comonad.hpp> |
| 16 | #include <boost/hana/config.hpp> |
| 17 | #include <boost/hana/core/dispatch.hpp> |
| 18 | |
| 19 | |
| 20 | namespace boost { namespace hana { |
| 21 | //! @cond |
| 22 | template <typename W_> |
| 23 | constexpr decltype(auto) extract_t::operator()(W_&& w) const { |
| 24 | using W = typename hana::tag_of<W_>::type; |
| 25 | using Extract = BOOST_HANA_DISPATCH_IF(extract_impl<W>, |
| 26 | hana::Comonad<W>::value |
| 27 | ); |
| 28 | |
| 29 | #ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS |
| 30 | static_assert(hana::Comonad<W>::value, |
| 31 | "hana::extract(w) requires 'w' to be a Comonad"); |
| 32 | #endif |
| 33 | |
| 34 | return Extract::apply(static_cast<W_&&>(w)); |
| 35 | } |
| 36 | //! @endcond |
| 37 | |
| 38 | template <typename W, bool condition> |
| 39 | struct extract_impl<W, when<condition>> : default_ { |
| 40 | template <typename ...Args> |
| 41 | static constexpr auto apply(Args&& ...args) = delete; |
| 42 | }; |
| 43 | }} // end namespace boost::hana |
| 44 | |
| 45 | #endif // !BOOST_HANA_EXTRACT_HPP |
| 46 |