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