1/*!
2@file
3Defines `boost::hana::drop_while`.
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_DROP_WHILE_HPP
11#define BOOST_HANA_DROP_WHILE_HPP
12
13#include <boost/hana/fwd/drop_while.hpp>
14
15#include <boost/hana/concept/foldable.hpp>
16#include <boost/hana/concept/iterable.hpp>
17#include <boost/hana/config.hpp>
18#include <boost/hana/core/dispatch.hpp>
19#include <boost/hana/detail/first_unsatisfied_index.hpp>
20#include <boost/hana/drop_front.hpp>
21#include <boost/hana/eval_if.hpp>
22#include <boost/hana/front.hpp>
23#include <boost/hana/is_empty.hpp>
24#include <boost/hana/lazy.hpp>
25
26
27namespace boost { namespace hana {
28 //! @cond
29 template <typename Xs, typename Pred>
30 constexpr auto drop_while_t::operator()(Xs&& xs, Pred&& pred) const {
31 using It = typename hana::tag_of<Xs>::type;
32 using DropWhile = BOOST_HANA_DISPATCH_IF(drop_while_impl<It>,
33 hana::Iterable<It>::value
34 );
35
36 #ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
37 static_assert(hana::Iterable<It>::value,
38 "hana::drop_while(xs, pred) requires 'xs' to be an Iterable");
39 #endif
40
41 return DropWhile::apply(static_cast<Xs&&>(xs), static_cast<Pred&&>(pred));
42 }
43 //! @endcond
44
45 namespace iterable_detail {
46 struct drop_while_helper {
47 struct next {
48 template <typename Xs, typename Pred>
49 constexpr decltype(auto) operator()(Xs&& xs, Pred&& pred) const {
50 return hana::drop_while(
51 hana::drop_front(static_cast<Xs&&>(xs)),
52 static_cast<Pred&&>(pred)
53 );
54 }
55 };
56
57 template <typename Xs, typename Pred>
58 constexpr decltype(auto) operator()(Xs&& xs, Pred&& pred) const {
59 return hana::eval_if(pred(hana::front(xs)),
60 hana::make_lazy(next{})(xs, pred),
61 hana::make_lazy(xs)
62 );
63 }
64 };
65 }
66
67 template <typename It, bool condition>
68 struct drop_while_impl<It, when<condition>> : default_ {
69 template <typename Xs, typename Pred>
70 static constexpr auto apply(Xs&& xs, Pred&& pred) {
71 return hana::eval_if(hana::is_empty(xs),
72 hana::make_lazy(xs),
73 hana::make_lazy(iterable_detail::drop_while_helper{})(
74 xs, static_cast<Pred&&>(pred))
75 );
76 }
77 };
78
79 template <typename S>
80 struct drop_while_impl<S, when<hana::Foldable<S>::value>> {
81 template <typename Xs, typename Pred>
82 static constexpr auto apply(Xs&& xs, Pred&&) {
83 using FirstUnsatisfied = decltype(
84 hana::unpack(static_cast<Xs&&>(xs),
85 detail::first_unsatisfied_index<Pred&&>{})
86 );
87 return hana::drop_front(static_cast<Xs&&>(xs),
88 FirstUnsatisfied{});
89 }
90 };
91}} // end namespace boost::hana
92
93#endif // !BOOST_HANA_DROP_WHILE_HPP
94

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