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Diffstat (limited to 'boost/hana/lift.hpp')
-rw-r--r-- | boost/hana/lift.hpp | 54 |
1 files changed, 54 insertions, 0 deletions
diff --git a/boost/hana/lift.hpp b/boost/hana/lift.hpp new file mode 100644 index 0000000000..a91c43bacc --- /dev/null +++ b/boost/hana/lift.hpp @@ -0,0 +1,54 @@ +/*! +@file +Defines `boost::hana::lift`. + +@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_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> + + +BOOST_HANA_NAMESPACE_BEGIN + template <typename A> + struct lift_t { + #ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS + static_assert(hana::Applicative<A>::value, + "hana::lift<A> requires 'A' to be an Applicative"); + #endif + + template <typename X> + constexpr auto operator()(X&& x) const { + using Lift = BOOST_HANA_DISPATCH_IF(lift_impl<A>, + hana::Applicative<A>::value + ); + + return Lift::apply(static_cast<X&&>(x)); + } + }; + + 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)); } + }; +BOOST_HANA_NAMESPACE_END + +#endif // !BOOST_HANA_LIFT_HPP |