1 // Copyright (c) Microsoft Open Technologies, Inc. All rights reserved. See License.txt in the project root for license information.
2
3 #pragma once
4
5 /*! \file rx-take_last.hpp
6
7 \brief Emit only the final t items emitted by the source Observable.
8
9 \tparam Count the type of the items counter.
10
11 \param t the number of last items to take.
12
13 \return An observable that emits only the last t items emitted by the source Observable, or all of the items from the source observable if that observable emits fewer than t items.
14
15 \sample
16 \snippet take_last.cpp take_last sample
17 \snippet output.txt take_last sample
18 */
19
20 #if !defined(RXCPP_OPERATORS_RX_TAKE_LAST_HPP)
21 #define RXCPP_OPERATORS_RX_TAKE_LAST_HPP
22
23 #include "../rx-includes.hpp"
24
25 namespace rxcpp {
26
27 namespace operators {
28
29 namespace detail {
30
31 template<class... AN>
32 struct take_last_invalid_arguments {};
33
34 template<class... AN>
35 struct take_last_invalid : public rxo::operator_base<take_last_invalid_arguments<AN...>> {
36 using type = observable<take_last_invalid_arguments<AN...>, take_last_invalid<AN...>>;
37 };
38 template<class... AN>
39 using take_last_invalid_t = typename take_last_invalid<AN...>::type;
40
41 template<class T, class Observable, class Count>
42 struct take_last : public operator_base<T>
43 {
44 typedef rxu::decay_t<Observable> source_type;
45 typedef rxu::decay_t<Count> count_type;
46
47 typedef std::queue<T> queue_type;
48 typedef typename queue_type::size_type queue_size_type;
49
50 struct values
51 {
valuesrxcpp::operators::detail::take_last::values52 values(source_type s, count_type t)
53 : source(std::move(s))
54 , count(static_cast<queue_size_type>(t))
55 {
56 }
57 source_type source;
58 queue_size_type count;
59 };
60 values initial;
61
take_lastrxcpp::operators::detail::take_last62 take_last(source_type s, count_type t)
63 : initial(std::move(s), std::move(t))
64 {
65 }
66
67 template<class Subscriber>
on_subscriberxcpp::operators::detail::take_last68 void on_subscribe(const Subscriber& s) const {
69
70 typedef Subscriber output_type;
71 struct state_type
72 : public std::enable_shared_from_this<state_type>
73 , public values
74 {
75 state_type(const values& i, const output_type& oarg)
76 : values(i)
77 , out(oarg)
78 {
79 }
80 queue_type items;
81 output_type out;
82 };
83 // take a copy of the values for each subscription
84 auto state = std::make_shared<state_type>(initial, s);
85
86 composite_subscription source_lifetime;
87
88 s.add(source_lifetime);
89
90 state->source.subscribe(
91 // split subscription lifetime
92 source_lifetime,
93 // on_next
94 [state, source_lifetime](T t) {
95 if(state->count > 0) {
96 if (state->items.size() == state->count) {
97 state->items.pop();
98 }
99 state->items.push(t);
100 }
101 },
102 // on_error
103 [state](rxu::error_ptr e) {
104 state->out.on_error(e);
105 },
106 // on_completed
107 [state]() {
108 while(!state->items.empty()) {
109 state->out.on_next(std::move(state->items.front()));
110 state->items.pop();
111 }
112 state->out.on_completed();
113 }
114 );
115 }
116 };
117
118 }
119
120 /*! @copydoc rx-take_last.hpp
121 */
122 template<class... AN>
take_last(AN &&...an)123 auto take_last(AN&&... an)
124 -> operator_factory<take_last_tag, AN...> {
125 return operator_factory<take_last_tag, AN...>(std::make_tuple(std::forward<AN>(an)...));
126 }
127
128 }
129
130 template<>
131 struct member_overload<take_last_tag>
132 {
133 template<class Observable,
134 class Count,
135 class Enabled = rxu::enable_if_all_true_type_t<
136 is_observable<Observable>>,
137 class SourceValue = rxu::value_type_t<Observable>,
138 class TakeLast = rxo::detail::take_last<SourceValue, rxu::decay_t<Observable>, rxu::decay_t<Count>>,
139 class Value = rxu::value_type_t<TakeLast>,
140 class Result = observable<Value, TakeLast>>
memberrxcpp::member_overload141 static Result member(Observable&& o, Count&& c) {
142 return Result(TakeLast(std::forward<Observable>(o), std::forward<Count>(c)));
143 }
144
145 template<class... AN>
memberrxcpp::member_overload146 static operators::detail::take_last_invalid_t<AN...> member(AN...) {
147 std::terminate();
148 return {};
149 static_assert(sizeof...(AN) == 10000, "take_last takes (Count)");
150 }
151 };
152
153 }
154
155 #endif
156