1/*!
2@file
3Defines `boost::hana::span`.
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_SPAN_HPP
11#define BOOST_HANA_SPAN_HPP
12
13#include <boost/hana/fwd/span.hpp>
14
15#include <boost/hana/at.hpp>
16#include <boost/hana/concept/sequence.hpp>
17#include <boost/hana/config.hpp>
18#include <boost/hana/core/dispatch.hpp>
19#include <boost/hana/core/make.hpp>
20#include <boost/hana/detail/nested_by.hpp> // required by fwd decl
21#include <boost/hana/detail/first_unsatisfied_index.hpp>
22#include <boost/hana/length.hpp>
23#include <boost/hana/pair.hpp>
24#include <boost/hana/unpack.hpp>
25
26#include <cstddef>
27#include <utility>
28
29
30namespace boost { namespace hana {
31 //! @cond
32 template <typename Xs, typename Pred>
33 constexpr auto span_t::operator()(Xs&& xs, Pred&& pred) const {
34 using S = typename hana::tag_of<Xs>::type;
35 using Span = BOOST_HANA_DISPATCH_IF(span_impl<S>,
36 hana::Sequence<S>::value
37 );
38
39 #ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
40 static_assert(hana::Sequence<S>::value,
41 "hana::span(xs, pred) requires 'xs' to be a Sequence");
42 #endif
43
44 return Span::apply(static_cast<Xs&&>(xs), static_cast<Pred&&>(pred));
45 }
46 //! @endcond
47
48 template <typename S, bool condition>
49 struct span_impl<S, when<condition>> : default_ {
50 template <typename Xs, std::size_t ...before, std::size_t ...after>
51 static constexpr auto span_helper(Xs&& xs, std::index_sequence<before...>,
52 std::index_sequence<after...>)
53 {
54 return hana::make_pair(
55 hana::make<S>(hana::at_c<before>(static_cast<Xs&&>(xs))...),
56 hana::make<S>(hana::at_c<sizeof...(before) + after>(static_cast<Xs&&>(xs))...)
57 );
58 }
59
60 template <typename Xs, typename Pred>
61 static constexpr auto apply(Xs&& xs, Pred&&) {
62 using FirstUnsatisfied = decltype(
63 hana::unpack(static_cast<Xs&&>(xs),
64 detail::first_unsatisfied_index<Pred&&>{})
65 );
66 constexpr std::size_t breakpoint = FirstUnsatisfied::value;
67 constexpr std::size_t N = decltype(hana::length(xs))::value;
68 return span_helper(static_cast<Xs&&>(xs),
69 std::make_index_sequence<breakpoint>{},
70 std::make_index_sequence<N - breakpoint>{});
71 }
72 };
73}} // end namespace boost::hana
74
75#endif // !BOOST_HANA_SPAN_HPP
76

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