Add ErrorOr to Nearby Platform

internal/platform/BUILD

@@ -45,6 +45,7 @@ cc_library(
         "byte_array.h",
         "callable.h",
         "exception.h",
+        "expected.h",
         "feature_flags.h",
         "input_stream.h",
         "listeners.h",
@@ -506,6 +507,7 @@ cc_test(
         "count_down_latch_test.cc",
         "crypto_test.cc",
         "direct_executor_test.cc",
+        "expected_test.cc",
         "future_test.cc",
         "multi_thread_executor_test.cc",
         "mutex_test.cc",

internal/platform/expected.h

@@ -0,0 +1,119 @@
+// Copyright 2024 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef PLATFORM_BASE_EXPECTED_H_
+#define PLATFORM_BASE_EXPECTED_H_
+
+#include <optional>
+#include <string>
+#include <utility>
+#include <variant>
+
+#include "proto/connections_enums.pb.h"
+
+namespace nearby {
+
+class Error {
+ public:
+  Error() = default;
+
+  explicit Error(location::nearby::proto::connections::OperationResultCode
+                     operation_result_code)
+      : operation_result_code_(operation_result_code) {}
+
+  bool success() const {
+    return operation_result_code_ == location::nearby::proto::connections::
+                                         OperationResultCode::DETAIL_SUCCESS;
+  }
+  bool failure() const { return !success(); }
+
+  std::optional<location::nearby::proto::connections::OperationResultCode>
+  operation_result_code() const {
+    return operation_result_code_;
+  }
+
+  static Error Success() { return Error(); }
+
+ private:
+  location::nearby::proto::connections::OperationResultCode
+      operation_result_code_ = location::nearby::proto::connections::
+          OperationResultCode::DETAIL_UNKNOWN;
+};
+
+// Forward declare.
+template <typename E>
+class Unexpected;
+
+template <typename T, typename E>
+class Expected {
+ public:
+  constexpr Expected(T value) : data_(std::move(value)) {}  // NOLINT
+  constexpr Expected(Unexpected<E> u);                      // NOLINT
+
+  constexpr operator bool() const {  // NOLINT
+    return has_value();
+  }
+
+  constexpr T& operator*() & { return value(); }
+  constexpr const T& operator*() const& { return value(); }
+  constexpr T&& operator*() && { return std::move(value()); }
+  constexpr const T& operator*() const&& { return std::move(value()); }
+
+  constexpr T* operator->() { return &value(); }
+  constexpr const T* operator->() const { return &value(); }
+
+  constexpr bool has_value() const { return std::holds_alternative<T>(data_); }
+  constexpr bool has_error() const { return std::holds_alternative<E>(data_); }
+
+  constexpr T& value() & { return std::get<T>(data_); }
+  constexpr const T& value() const& { return std::get<T>(data_); }
+  constexpr T&& value() && { return std::get<T>(std::move(data_)); }
+  constexpr const T& value() const&& { return std::get<T>(std::move(data_)); }
+
+  constexpr E& error() & { return std::get<E>(data_); }
+  constexpr const E& error() const& { return std::get<E>(data_); }
+  constexpr E&& error() && { return std::get<E>(std::move(data_)); }
+  constexpr const E&& error() const&& { return std::get<E>(std::move(data_)); }
+
+ private:
+  std::variant<T, E> data_;
+};
+
+template <typename E>
+class Unexpected {
+ public:
+  constexpr Unexpected(E error) : error_(std::move(error)) {}  // NOLINT
+
+ private:
+  template <typename, typename>
+  friend class Expected;
+
+  E error_;
+};
+
+Unexpected(const char*) -> Unexpected<std::string>;
+
+template <typename T, typename E>
+constexpr Expected<T, E>::Expected(Unexpected<E> u)
+    : data_(std::move(u.error_)) {}
+
+template <typename T>
+class ErrorOr : public Expected<T, Error> {
+ public:
+  using Expected<T, Error>::Expected;
+};
+
+}  // namespace nearby
+
+#endif  // PLATFORM_BASE_EXPECTED_H_

internal/platform/expected_test.cc

@@ -0,0 +1,51 @@
+// Copyright 2024 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "internal/platform/expected.h"
+
+#include <memory>
+
+#include "gtest/gtest.h"
+#include "proto/connections_enums.pb.h"
+
+namespace nearby {
+using ::location::nearby::proto::connections::OperationResultCode;
+
+TEST(ExpectedTest, Expected) {
+  ErrorOr<int> value = 42;
+  EXPECT_TRUE(value.has_value());
+  EXPECT_FALSE(value.has_error());
+  EXPECT_EQ(*value, 42);
+
+  ErrorOr<int> error{Error(OperationResultCode::DETAIL_UNKNOWN)};
+  EXPECT_FALSE(error.has_value());
+  EXPECT_TRUE(error.has_error());
+  EXPECT_EQ(error.error().operation_result_code(),
+            OperationResultCode::DETAIL_UNKNOWN);
+
+  ErrorOr<std::unique_ptr<int>> value2{std::make_unique<int>(42)};
+  EXPECT_TRUE(value2.has_value());
+  EXPECT_FALSE(value2.has_error());
+  EXPECT_NE(value2.value().get(), nullptr);
+  EXPECT_EQ(*value2.value(), 42);
+
+  ErrorOr<std::unique_ptr<int>> error2{
+      Error(OperationResultCode::IO_FILE_OPENING_ERROR)};
+  EXPECT_FALSE(error2.has_value());
+  EXPECT_TRUE(error2.has_error());
+  EXPECT_EQ(error2.error().operation_result_code(),
+            OperationResultCode::IO_FILE_OPENING_ERROR);
+}
+
+}  // namespace nearby