63e88f80
 Hu Chunming
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/*!
@file
Defines `boost::hana::lift`.
Copyright Louis Dionne 2013-2022
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_LIFT_HPP
#define BOOST_HANA_LIFT_HPP
#include <boost/hana/fwd/lift.hpp>
#include <boost/hana/concept/applicative.hpp>
#include <boost/hana/concept/sequence.hpp>
#include <boost/hana/config.hpp>
#include <boost/hana/core/dispatch.hpp>
#include <boost/hana/core/make.hpp>
namespace boost { namespace hana {
//! @cond
template <typename A>
template <typename X>
constexpr auto lift_t<A>::operator()(X&& x) const {
#ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
static_assert(hana::Applicative<A>::value,
"hana::lift<A> requires 'A' to be an Applicative");
#endif
using Lift = BOOST_HANA_DISPATCH_IF(lift_impl<A>,
hana::Applicative<A>::value
);
return Lift::apply(static_cast<X&&>(x));
}
//! @endcond
template <typename A, bool condition>
struct lift_impl<A, when<condition>> : default_ {
template <typename ...Args>
static constexpr auto apply(Args&& ...args) = delete;
};
template <typename S>
struct lift_impl<S, when<Sequence<S>::value>> {
template <typename X>
static constexpr decltype(auto) apply(X&& x)
{ return hana::make<S>(static_cast<X&&>(x)); }
};
}} // end namespace boost::hana
#endif // !BOOST_HANA_LIFT_HPP
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