1 /*
2 * Copyright (C) 2018 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17 #ifndef IDMAP2_INCLUDE_IDMAP2_RESULT_H_
18 #define IDMAP2_INCLUDE_IDMAP2_RESULT_H_
19
20 #include <string>
21 #include <utility>
22 #include <variant>
23
24 #include "android-base/logging.h" // CHECK
25
26 namespace android::idmap2 {
27
28 using Unit = std::monostate;
29
30 class Error {
31 public:
32 explicit Error(const Error& parent) = default;
33
34 // NOLINTNEXTLINE(cert-dcl50-cpp)
35 explicit Error(const char* fmt, ...) __attribute__((__format__(printf, 2, 3)));
36
37 // NOLINTNEXTLINE(cert-dcl50-cpp)
38 explicit Error(const Error& parent, const char* fmt, ...)
39 __attribute__((__format__(printf, 3, 4)));
40
GetMessage()41 inline std::string GetMessage() const {
42 return msg_;
43 }
44
45 private:
46 std::string msg_;
47 };
48
49 template <typename T>
50 class Result {
51 public:
52 Result(const T& value); // NOLINT(runtime/explicit)
53 Result(T&& value) noexcept; // NOLINT(runtime/explicit)
54
55 Result(const Error& error); // NOLINT(runtime/explicit)
56 Result(Error&& error) noexcept; // NOLINT(runtime/explicit)
57
58 Result(const Result& error) = default;
59
60 Result& operator=(const Result& rhs) = default;
61 Result& operator=(Result&& rhs) noexcept = default;
62
63 explicit operator bool() const;
64
65 constexpr const T& operator*() const&;
66 T& operator*() &;
67
68 constexpr const T* operator->() const&;
69 T* operator->() &;
70
71 std::string GetErrorMessage() const;
72 Error GetError() const;
73
74 private:
75 bool is_ok() const;
76
77 std::variant<T, Error> data_;
78 };
79
80 template <typename T>
Result(const T & value)81 Result<T>::Result(const T& value) : data_(std::in_place_type<T>, value) {
82 }
83
84 template <typename T>
Result(T && value)85 Result<T>::Result(T&& value) noexcept : data_(std::in_place_type<T>, std::forward<T>(value)) {
86 }
87
88 template <typename T>
Result(const Error & error)89 Result<T>::Result(const Error& error) : data_(std::in_place_type<Error>, error) {
90 }
91
92 template <typename T>
Result(Error && error)93 Result<T>::Result(Error&& error) noexcept
94 : data_(std::in_place_type<Error>, std::forward<Error>(error)) {
95 }
96
97 template <typename T>
98 Result<T>::operator bool() const {
99 return is_ok();
100 }
101
102 template <typename T>
103 constexpr const T& Result<T>::operator*() const& {
104 CHECK(is_ok()) << "Result<T>::operator* called in ERROR state";
105 return std::get<T>(data_);
106 }
107
108 template <typename T>
109 T& Result<T>::operator*() & {
110 CHECK(is_ok()) << "Result<T>::operator* called in ERROR state";
111 return std::get<T>(data_);
112 }
113
114 template <typename T>
115 constexpr const T* Result<T>::operator->() const& {
116 CHECK(is_ok()) << "Result<T>::operator-> called in ERROR state";
117 return &std::get<T>(data_);
118 }
119
120 template <typename T>
121 T* Result<T>::operator->() & {
122 CHECK(is_ok()) << "Result<T>::operator-> called in ERROR state";
123 return &std::get<T>(data_);
124 }
125
126 template <typename T>
GetErrorMessage()127 inline std::string Result<T>::GetErrorMessage() const {
128 CHECK(!is_ok()) << "Result<T>::GetErrorMessage called in OK state";
129 return std::get<Error>(data_).GetMessage();
130 }
131
132 template <typename T>
GetError()133 inline Error Result<T>::GetError() const {
134 CHECK(!is_ok()) << "Result<T>::GetError called in OK state";
135 return Error(std::get<Error>(data_));
136 }
137
138 template <typename T>
is_ok()139 inline bool Result<T>::is_ok() const {
140 return std::holds_alternative<T>(data_);
141 }
142
143 } // namespace android::idmap2
144
145 #endif // IDMAP2_INCLUDE_IDMAP2_RESULT_H_
146