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/*!
@file
Defines `boost::hana::extract`.
@copyright Louis Dionne 2013-2016
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
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