75 lines
2.4 KiB
C++
75 lines
2.4 KiB
C++
/*!
|
|
@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
|