1/*!
2@file
3Defines `boost::hana::append`.
4
5Copyright Louis Dionne 2013-2022
6Distributed under the Boost Software License, Version 1.0.
7(See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
8 */
9
10#ifndef BOOST_HANA_APPEND_HPP
11#define BOOST_HANA_APPEND_HPP
12
13#include <boost/hana/fwd/append.hpp>
14
15#include <boost/hana/at.hpp>
16#include <boost/hana/concat.hpp>
17#include <boost/hana/concept/monad_plus.hpp>
18#include <boost/hana/concept/sequence.hpp>
19#include <boost/hana/config.hpp>
20#include <boost/hana/core/dispatch.hpp>
21#include <boost/hana/core/make.hpp>
22#include <boost/hana/length.hpp>
23#include <boost/hana/lift.hpp>
24
25#include <cstddef>
26#include <utility>
27
28
29namespace boost { namespace hana {
30 //! @cond
31 template <typename Xs, typename X>
32 constexpr auto append_t::operator()(Xs&& xs, X&& x) const {
33 using M = typename hana::tag_of<Xs>::type;
34 using Append = BOOST_HANA_DISPATCH_IF(append_impl<M>,
35 hana::MonadPlus<M>::value
36 );
37
38 #ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
39 static_assert(hana::MonadPlus<M>::value,
40 "hana::append(xs, x) requires 'xs' to be a MonadPlus");
41 #endif
42
43 return Append::apply(static_cast<Xs&&>(xs), static_cast<X&&>(x));
44 }
45 //! @endcond
46
47 template <typename M, bool condition>
48 struct append_impl<M, when<condition>> : default_ {
49 template <typename Xs, typename X>
50 static constexpr auto apply(Xs&& xs, X&& x) {
51 return hana::concat(static_cast<Xs&&>(xs),
52 hana::lift<M>(static_cast<X&&>(x)));
53 }
54 };
55
56 template <typename S>
57 struct append_impl<S, when<Sequence<S>::value>> {
58 template <typename Xs, typename X, std::size_t ...i>
59 static constexpr auto append_helper(Xs&& xs, X&& x, std::index_sequence<i...>) {
60 return hana::make<S>(
61 hana::at_c<i>(static_cast<Xs&&>(xs))..., static_cast<X&&>(x)
62 );
63 }
64
65 template <typename Xs, typename X>
66 static constexpr auto apply(Xs&& xs, X&& x) {
67 constexpr std::size_t N = decltype(hana::length(xs))::value;
68 return append_helper(static_cast<Xs&&>(xs), static_cast<X&&>(x),
69 std::make_index_sequence<N>{});
70 }
71 };
72}} // end namespace boost::hana
73
74#endif // !BOOST_HANA_APPEND_HPP
75

source code of boost/libs/hana/include/boost/hana/append.hpp