/*! @file Defines `boost::hana::prefix`. @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_PREFIX_HPP #define BOOST_HANA_PREFIX_HPP #include <boost/hana/fwd/prefix.hpp> #include <boost/hana/append.hpp> #include <boost/hana/chain.hpp> #include <boost/hana/concept/monad_plus.hpp> #include <boost/hana/config.hpp> #include <boost/hana/core/dispatch.hpp> #include <boost/hana/functional/partial.hpp> #include <boost/hana/lift.hpp> BOOST_HANA_NAMESPACE_BEGIN //! @cond template <typename Xs, typename Pref> constexpr auto prefix_t::operator()(Xs&& xs, Pref&& pref) const { using M = typename hana::tag_of<Xs>::type; using Prefix = BOOST_HANA_DISPATCH_IF(prefix_impl<M>, hana::MonadPlus<M>::value ); #ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS static_assert(hana::MonadPlus<M>::value, "hana::prefix(xs, pref) requires 'xs' to be a MonadPlus"); #endif return Prefix::apply(static_cast<Xs&&>(xs), static_cast<Pref&&>(pref)); } //! @endcond template <typename M, bool condition> struct prefix_impl<M, when<condition>> : default_ { template <typename Xs, typename Z> static constexpr decltype(auto) apply(Xs&& xs, Z&& z) { return hana::chain(static_cast<Xs&&>(xs), hana::partial(hana::append, hana::lift<M>(static_cast<Z&&>(z)))); } }; BOOST_HANA_NAMESPACE_END #endif // !BOOST_HANA_PREFIX_HPP