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-rw-r--r--boost/hana/prepend.hpp74
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+/*!
+@file
+Defines `boost::hana::prepend`.
+
+@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_PREPEND_HPP
+#define BOOST_HANA_PREPEND_HPP
+
+#include <boost/hana/fwd/prepend.hpp>
+
+#include <boost/hana/at.hpp>
+#include <boost/hana/concat.hpp>
+#include <boost/hana/concept/monad_plus.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/length.hpp>
+#include <boost/hana/lift.hpp>
+
+#include <cstddef>
+#include <utility>
+
+
+BOOST_HANA_NAMESPACE_BEGIN
+ //! @cond
+ template <typename Xs, typename X>
+ constexpr auto prepend_t::operator()(Xs&& xs, X&& x) const {
+ using M = typename hana::tag_of<Xs>::type;
+ using Prepend = BOOST_HANA_DISPATCH_IF(prepend_impl<M>,
+ hana::MonadPlus<M>::value
+ );
+
+ #ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
+ static_assert(hana::MonadPlus<M>::value,
+ "hana::prepend(xs, x) requires 'xs' to be a MonadPlus");
+ #endif
+
+ return Prepend::apply(static_cast<Xs&&>(xs), static_cast<X&&>(x));
+ }
+ //! @endcond
+
+ template <typename M, bool condition>
+ struct prepend_impl<M, when<condition>> : default_ {
+ template <typename Xs, typename X>
+ static constexpr auto apply(Xs&& xs, X&& x) {
+ return hana::concat(hana::lift<M>(static_cast<X&&>(x)),
+ static_cast<Xs&&>(xs));
+ }
+ };
+
+ template <typename S>
+ struct prepend_impl<S, when<Sequence<S>::value>> {
+ template <typename Xs, typename X, std::size_t ...i>
+ static constexpr auto prepend_helper(Xs&& xs, X&& x, std::index_sequence<i...>) {
+ return hana::make<S>(
+ static_cast<X&&>(x), hana::at_c<i>(static_cast<Xs&&>(xs))...
+ );
+ }
+
+ template <typename Xs, typename X>
+ static constexpr auto apply(Xs&& xs, X&& x) {
+ constexpr std::size_t N = decltype(hana::length(xs))::value;
+ return prepend_helper(static_cast<Xs&&>(xs), static_cast<X&&>(x),
+ std::make_index_sequence<N>{});
+ }
+ };
+BOOST_HANA_NAMESPACE_END
+
+#endif // !BOOST_HANA_PREPEND_HPP