55 lines
1.5 KiB
C++
55 lines
1.5 KiB
C++
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/*!
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@file
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Defines `boost::hana::lift`.
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@copyright Louis Dionne 2013-2016
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Distributed under the Boost Software License, Version 1.0.
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(See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
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*/
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#ifndef BOOST_HANA_LIFT_HPP
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#define BOOST_HANA_LIFT_HPP
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#include <boost/hana/fwd/lift.hpp>
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#include <boost/hana/concept/applicative.hpp>
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#include <boost/hana/concept/sequence.hpp>
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#include <boost/hana/config.hpp>
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#include <boost/hana/core/dispatch.hpp>
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#include <boost/hana/core/make.hpp>
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BOOST_HANA_NAMESPACE_BEGIN
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template <typename A>
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struct lift_t {
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#ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
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static_assert(hana::Applicative<A>::value,
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"hana::lift<A> requires 'A' to be an Applicative");
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#endif
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template <typename X>
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constexpr auto operator()(X&& x) const {
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using Lift = BOOST_HANA_DISPATCH_IF(lift_impl<A>,
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hana::Applicative<A>::value
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);
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return Lift::apply(static_cast<X&&>(x));
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}
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};
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template <typename A, bool condition>
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struct lift_impl<A, when<condition>> : default_ {
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template <typename ...Args>
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static constexpr auto apply(Args&& ...args) = delete;
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};
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template <typename S>
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struct lift_impl<S, when<Sequence<S>::value>> {
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template <typename X>
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static constexpr decltype(auto) apply(X&& x)
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{ return hana::make<S>(static_cast<X&&>(x)); }
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};
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BOOST_HANA_NAMESPACE_END
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#endif // !BOOST_HANA_LIFT_HPP
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