53 lines
1.6 KiB
C++
53 lines
1.6 KiB
C++
|
/*!
|
||
|
|
@file
|
||
|
|
Defines `boost::hana::prefix`.
|
||
|
|
|
||
|
|
@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_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
|