/*! @file Defines `boost::hana::extract`. @copyright Louis Dionne 2013-2017 Distributed under the Boost Software License, Version 1.0. (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt) */ #ifndef BOOST_HANA_EXTRACT_HPP #define BOOST_HANA_EXTRACT_HPP #include <boost/hana/fwd/extract.hpp> #include <boost/hana/concept/comonad.hpp> #include <boost/hana/config.hpp> #include <boost/hana/core/dispatch.hpp> BOOST_HANA_NAMESPACE_BEGIN //! @cond template <typename W_> constexpr decltype(auto) extract_t::operator()(W_&& w) const { using W = typename hana::tag_of<W_>::type; using Extract = BOOST_HANA_DISPATCH_IF(extract_impl<W>, hana::Comonad<W>::value ); #ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS static_assert(hana::Comonad<W>::value, "hana::extract(w) requires 'w' to be a Comonad"); #endif return Extract::apply(static_cast<W_&&>(w)); } //! @endcond template <typename W, bool condition> struct extract_impl<W, when<condition>> : default_ { template <typename ...Args> static constexpr auto apply(Args&& ...args) = delete; }; BOOST_HANA_NAMESPACE_END #endif // !BOOST_HANA_EXTRACT_HPP