1//===----------------------------------------------------------------------===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8
9// UNSUPPORTED: c++03, c++11, c++14, c++17, c++20
10
11// <expected>
12
13// template<class F> constexpr auto and_then(F&& f) &;
14// template<class F> constexpr auto and_then(F&& f) const &;
15// template<class F> constexpr auto and_then(F&& f) &&;
16// template<class F> constexpr auto and_then(F&& f) const &&;
17
18#include <cassert>
19#include <concepts>
20#include <expected>
21#include <memory>
22#include <type_traits>
23#include <utility>
24
25#include "../../types.h"
26
27struct LVal {
28 constexpr std::expected<int, int> operator()(int&) { return 1; }
29 std::expected<int, int> operator()(const int&) = delete;
30 std::expected<int, int> operator()(int&&) = delete;
31 std::expected<int, int> operator()(const int&&) = delete;
32};
33
34struct CLVal {
35 std::expected<int, int> operator()(int&) = delete;
36 constexpr std::expected<int, int> operator()(const int&) { return 1; }
37 std::expected<int, int> operator()(int&&) = delete;
38 std::expected<int, int> operator()(const int&&) = delete;
39};
40
41struct RVal {
42 std::expected<int, int> operator()(int&) = delete;
43 std::expected<int, int> operator()(const int&) = delete;
44 constexpr std::expected<int, int> operator()(int&&) { return 1; }
45 std::expected<int, int> operator()(const int&&) = delete;
46};
47
48struct CRVal {
49 std::expected<int, int> operator()(int&) = delete;
50 std::expected<int, int> operator()(const int&) = delete;
51 std::expected<int, int> operator()(int&&) = delete;
52 constexpr std::expected<int, int> operator()(const int&&) { return 1; }
53};
54
55struct RefQual {
56 constexpr std::expected<int, int> operator()(int) & { return 1; }
57 std::expected<int, int> operator()(int) const& = delete;
58 std::expected<int, int> operator()(int) && = delete;
59 std::expected<int, int> operator()(int) const&& = delete;
60};
61
62struct CRefQual {
63 std::expected<int, int> operator()(int) & = delete;
64 constexpr std::expected<int, int> operator()(int) const& { return 1; }
65 std::expected<int, int> operator()(int) && = delete;
66 std::expected<int, int> operator()(int) const&& = delete;
67};
68
69struct RVRefQual {
70 std::expected<int, int> operator()(int) & = delete;
71 std::expected<int, int> operator()(int) const& = delete;
72 constexpr std::expected<int, int> operator()(int) && { return 1; }
73 std::expected<int, int> operator()(int) const&& = delete;
74};
75
76struct RVCRefQual {
77 std::expected<int, int> operator()(int) & = delete;
78 std::expected<int, int> operator()(int) const& = delete;
79 std::expected<int, int> operator()(int) && = delete;
80 constexpr std::expected<int, int> operator()(int) const&& { return 1; }
81};
82
83struct UnexpectedLVal {
84 constexpr std::expected<int, int> operator()(int&) { return std::expected<int, int>(std::unexpected<int>(5)); }
85 std::expected<int, int> operator()(const int&) = delete;
86 std::expected<int, int> operator()(int&&) = delete;
87 std::expected<int, int> operator()(const int&&) = delete;
88};
89
90struct UnexpectedCLVal {
91 std::expected<int, int> operator()(int&) = delete;
92 constexpr std::expected<int, int> operator()(const int&) { return std::expected<int, int>(std::unexpected<int>(5)); }
93 std::expected<int, int> operator()(int&&) = delete;
94 std::expected<int, int> operator()(const int&&) = delete;
95};
96
97struct UnexpectedRVal {
98 std::expected<int, int> operator()(int&) = delete;
99 std::expected<int, int> operator()(const int&) = delete;
100 constexpr std::expected<int, int> operator()(int&&) { return std::expected<int, int>(std::unexpected<int>(5)); }
101 std::expected<int, int> operator()(const int&&) = delete;
102};
103
104struct UnexpectedCRVal {
105 std::expected<int, int> operator()(int&) = delete;
106 std::expected<int, int> operator()(const int&) = delete;
107 std::expected<int, int> operator()(int&&) = delete;
108 constexpr std::expected<int, int> operator()(const int&&) { return std::expected<int, int>(std::unexpected<int>(5)); }
109};
110
111struct UnexpectedRefQual {
112 constexpr std::expected<int, int> operator()(int) & { return std::expected<int, int>(std::unexpected<int>(5)); }
113 std::expected<int, int> operator()(int) const& = delete;
114 std::expected<int, int> operator()(int) && = delete;
115 std::expected<int, int> operator()(int) const&& = delete;
116};
117
118struct UnexpectedCRefQual {
119 std::expected<int, int> operator()(int) & = delete;
120 constexpr std::expected<int, int> operator()(int) const& { return std::expected<int, int>(std::unexpected<int>(5)); }
121 std::expected<int, int> operator()(int) && = delete;
122 std::expected<int, int> operator()(int) const&& = delete;
123};
124
125struct UnexpectedRVRefQual {
126 std::expected<int, int> operator()(int) & = delete;
127 std::expected<int, int> operator()(int) const& = delete;
128 constexpr std::expected<int, int> operator()(int) && { return std::expected<int, int>(std::unexpected<int>(5)); }
129 std::expected<int, int> operator()(int) const&& = delete;
130};
131
132struct UnexpectedRVCRefQual {
133 std::expected<int, int> operator()(int) & = delete;
134 std::expected<int, int> operator()(int) const& = delete;
135 std::expected<int, int> operator()(int) && = delete;
136 constexpr std::expected<int, int> operator()(int) const&& { return std::expected<int, int>(std::unexpected<int>(5)); }
137};
138
139struct NonCopyable {
140 constexpr NonCopyable(int) {}
141 NonCopyable(const NonCopyable&) = delete;
142};
143
144struct NonMovable {
145 constexpr NonMovable(int) {}
146 NonMovable(NonMovable&&) = delete;
147};
148
149struct NonConst {
150 std::expected<int, int> non_const() { return 1; }
151};
152
153template <class E, class F>
154concept has_and_then = requires(E&& e, F&& f) {
155 {std::forward<E>(e).and_then(std::forward<F>(f))};
156};
157
158// clang-format off
159static_assert( has_and_then<std::expected<int, int>&, std::expected<int, int>(int&)>);
160static_assert(!has_and_then<std::expected<int, NonCopyable>&, std::expected<int, NonCopyable>(int&)>);
161static_assert( has_and_then<const std::expected<int, int>&, std::expected<int, int>(const int&)>);
162static_assert(!has_and_then<const std::expected<int, NonCopyable>&, std::expected<int, NonCopyable>(const int&)>);
163static_assert( has_and_then<std::expected<int, int>&&, std::expected<int, int>(int)>);
164static_assert(!has_and_then<std::expected<int, NonMovable>&&, std::expected<int, NonMovable>(int)>);
165static_assert( has_and_then<const std::expected<int, int>&&, std::expected<int, int>(const int)>);
166static_assert(!has_and_then<const std::expected<int, NonMovable>&&, std::expected<int, NonMovable>(const int)>);
167
168// [LWG 3877] https://cplusplus.github.io/LWG/issue3877, check constraint failing but not compile error inside the function body.
169static_assert(!has_and_then<const std::expected<int, std::unique_ptr<int>>&, int()>);
170static_assert(!has_and_then<const std::expected<int, std::unique_ptr<int>>&&, int()>);
171
172// [LWG 3983] https://cplusplus.github.io/LWG/issue3938, check std::expected monadic ops well-formed with move-only error_type.
173// There are no effects for `&` and `const &` overload, because the constraints requires is_constructible_v<E, decltype(error())> is true.
174static_assert(has_and_then<std::expected<int, MoveOnlyErrorType>&&, std::expected<int, MoveOnlyErrorType>(int)>);
175static_assert(has_and_then<const std::expected<int, MoveOnlyErrorType>&&, std::expected<int, MoveOnlyErrorType>(const int)>);
176
177constexpr void test_val_types() {
178 // Test & overload
179 {
180 // Without & qualifier on F's operator()
181 {
182 std::expected<int, int> e{0};
183 std::same_as<std::expected<int, int>> decltype(auto) val = e.and_then(LVal{});
184 assert(val == 1);
185 assert(e.and_then(UnexpectedLVal{}).error() == 5);
186 }
187
188 // With & qualifier on F's operator()
189 {
190 std::expected<int, int> e{0};
191 RefQual l{};
192 std::same_as<std::expected<int, int>> decltype(auto) val = e.and_then(l);
193 assert(val == 1);
194 UnexpectedRefQual nl{};
195 assert(e.and_then(nl).error() == 5);
196 }
197 }
198
199 // Test const& overload
200 {
201 // Without & qualifier on F's operator()
202 {
203 const std::expected<int, int> e{0};
204 std::same_as<std::expected<int, int>> decltype(auto) val = e.and_then(CLVal{});
205 assert(val == 1);
206 assert(e.and_then(UnexpectedCLVal{}).error() == 5);
207 }
208
209 // With & qualifier on F's operator()
210 {
211 const std::expected<int, int> e{0};
212 const CRefQual l{};
213 std::same_as<std::expected<int, int>> decltype(auto) val = e.and_then(l);
214 assert(val == 1);
215 const UnexpectedCRefQual nl{};
216 assert(e.and_then(nl).error() == 5);
217 }
218 }
219
220 // Test && overload
221 {
222 // Without & qualifier on F's operator()
223 {
224 std::expected<int, int> e{0};
225 std::same_as<std::expected<int, int>> decltype(auto) val = std::move(e).and_then(RVal{});
226 assert(val == 1);
227 assert(std::move(e).and_then(UnexpectedRVal{}).error() == 5);
228 }
229
230 // With & qualifier on F's operator()
231 {
232 std::expected<int, int> e{0};
233 std::same_as<std::expected<int, int>> decltype(auto) val = std::move(e).and_then(RVRefQual{});
234 assert(val == 1);
235 assert(e.and_then(UnexpectedRVRefQual{}).error() == 5);
236 }
237 }
238
239 // Test const&& overload
240 {
241 // Without & qualifier on F's operator()
242 {
243 const std::expected<int, int> e{0};
244 std::same_as<std::expected<int, int>> decltype(auto) val = std::move(e).and_then(CRVal{});
245 assert(val == 1);
246 assert(std::move(e).and_then(UnexpectedCRVal{}).error() == 5);
247 }
248
249 // With & qualifier on F's operator()
250 {
251 const std::expected<int, int> e{0};
252 const RVCRefQual l{};
253 std::same_as<std::expected<int, int>> decltype(auto) val = std::move(e).and_then(std::move(l));
254 assert(val == 1);
255 const UnexpectedRVCRefQual nl{};
256 assert(std::move(e).and_then(std::move(nl)).error() == 5);
257 }
258 }
259}
260// clang-format on
261
262// check that the lambda body is not instantiated during overload resolution
263constexpr void test_sfinae() {
264 std::expected<NonConst, int> e(std::unexpected<int>(2));
265 auto l = [](auto&& x) { return x.non_const(); };
266 (void)e.and_then(l);
267 (void)std::move(e).and_then(l);
268}
269
270constexpr void test_move_only_error_type() {
271 // Test &&
272 {
273 std::expected<int, MoveOnlyErrorType> e;
274 auto l = [](int) { return std::expected<int, MoveOnlyErrorType>{}; };
275 (void)std::move(e).and_then(l);
276 }
277
278 // Test const&&
279 {
280 const std::expected<int, MoveOnlyErrorType> e;
281 auto l = [](const int) { return std::expected<int, MoveOnlyErrorType>{}; };
282 (void)std::move(e).and_then(l);
283 }
284}
285
286constexpr bool test() {
287 test_sfinae();
288 test_val_types();
289 test_move_only_error_type();
290
291 std::expected<int, int> e(std::unexpected<int>(1));
292 const auto& ce = e;
293
294 const auto never_called = [](int) {
295 assert(false);
296 return std::expected<int, int>();
297 };
298
299 (void)e.and_then(never_called);
300 (void)std::move(e).and_then(never_called);
301 (void)ce.and_then(never_called);
302 (void)std::move(ce).and_then(never_called);
303
304 return true;
305}
306
307int main(int, char**) {
308 test();
309 static_assert(test());
310
311 return 0;
312}
313

source code of libcxx/test/std/utilities/expected/expected.expected/monadic/and_then.pass.cpp