update sources to v12.2.3

[ceph.git] / ceph / src / boost / boost / hana / take_front.hpp

diff --git a/ceph/src/boost/boost/hana/take_front.hpp b/ceph/src/boost/boost/hana/take_front.hpp
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+/*!
+@file
+Defines `boost::hana::take_front` and `boost::hana::take_front_c`.
+
+@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_TAKE_FRONT_HPP
+#define BOOST_HANA_TAKE_FRONT_HPP
+
+#include <boost/hana/fwd/take_front.hpp>
+
+#include <boost/hana/at.hpp>
+#include <boost/hana/concept/integral_constant.hpp>
+#include <boost/hana/concept/sequence.hpp>
+#include <boost/hana/config.hpp>
+#include <boost/hana/core/dispatch.hpp>
+#include <boost/hana/core/make.hpp>
+#include <boost/hana/integral_constant.hpp>
+#include <boost/hana/length.hpp>
+
+#include <cstddef>
+#include <utility>
+
+
+BOOST_HANA_NAMESPACE_BEGIN
+    //! @cond
+    template <typename Xs, typename N>
+    constexpr auto take_front_t::operator()(Xs&& xs, N const& n) const {
+        using S = typename hana::tag_of<Xs>::type;
+        using TakeFront = BOOST_HANA_DISPATCH_IF(take_front_impl<S>,
+            hana::Sequence<S>::value &&
+            hana::IntegralConstant<N>::value
+        );
+
+#ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
+        static_assert(hana::Sequence<S>::value,
+        "hana::take_front(xs, n) requires 'xs' to be a Sequence");
+
+        static_assert(hana::IntegralConstant<N>::value,
+        "hana::take_front(xs, n) requires 'n' to be an IntegralConstant");
+#endif
+
+        return TakeFront::apply(static_cast<Xs&&>(xs), n);
+    }
+    //! @endcond
+
+    template <typename S, bool condition>
+    struct take_front_impl<S, when<condition>> : default_ {
+        template <typename Xs, std::size_t ...n>
+        static constexpr auto take_front_helper(Xs&& xs, std::index_sequence<n...>) {
+            return hana::make<S>(hana::at_c<n>(static_cast<Xs&&>(xs))...);
+        }
+
+        template <typename Xs, typename N>
+        static constexpr auto apply(Xs&& xs, N const&) {
+            constexpr std::size_t n = N::value;
+            constexpr std::size_t size = decltype(hana::length(xs))::value;
+            return take_front_helper(static_cast<Xs&&>(xs),
+                        std::make_index_sequence<(n < size ? n : size)>{});
+        }
+    };
+
+    template <std::size_t n>
+    struct take_front_c_t {
+        template <typename Xs>
+        constexpr auto operator()(Xs&& xs) const {
+            return hana::take_front(static_cast<Xs&&>(xs), hana::size_c<n>);
+        }
+    };
+BOOST_HANA_NAMESPACE_END
+
+#endif // !BOOST_HANA_TAKE_FRONT_HPP