1 /*
2  * Copyright (C) 2019 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 
18 #pragma once
19 
20 #include <string>
21 #include <variant>
22 
23 #include <android-base/logging.h>
24 
25 namespace android {
26 namespace jsonpb {
27 
28 template <typename T>
29 struct ErrorOr {
30     template <class... Args>
ErrorOrErrorOr31     explicit ErrorOr(Args&&... args) : data_(kIndex1, std::forward<Args>(args)...) {}
32     T& operator*() {
33         CHECK(ok());
34         return *std::get_if<1u>(&data_);
35     }
36     const T& operator*() const {
37         CHECK(ok());
38         return *std::get_if<1u>(&data_);
39     }
40     T* operator->() {
41         CHECK(ok());
42         return std::get_if<1u>(&data_);
43     }
44     const T* operator->() const {
45         CHECK(ok());
46         return std::get_if<1u>(&data_);
47     }
errorErrorOr48     const std::string& error() const {
49         CHECK(!ok());
50         return *std::get_if<0u>(&data_);
51     }
okErrorOr52     bool ok() const { return data_.index() != 0; }
MakeErrorErrorOr53     static ErrorOr<T> MakeError(const std::string& message) {
54         return ErrorOr<T>(message, Tag::kDummy);
55     }
56 
57   private:
58     enum class Tag { kDummy };
59     static constexpr std::in_place_index_t<0> kIndex0{};
60     static constexpr std::in_place_index_t<1> kIndex1{};
ErrorOrErrorOr61     ErrorOr(const std::string& msg, Tag) : data_(kIndex0, msg) {}
62 
63     std::variant<std::string, T> data_;
64 };
65 
66 template <typename T>
MakeError(const std::string & message)67 inline ErrorOr<T> MakeError(const std::string& message) {
68     return ErrorOr<T>::MakeError(message);
69 }
70 
71 }  // namespace jsonpb
72 }  // namespace android
73