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)67inline ErrorOr<T> MakeError(const std::string& message) { 68 return ErrorOr<T>::MakeError(message); 69 } 70 71 } // namespace jsonpb 72 } // namespace android 73