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* Copyright (C) 2017 The Android Open Source Project
* 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
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* See the License for the specific language governing permissions and
* limitations under the License.
#include <cassert>
#include "netdutils/Status.h"
namespace android {
namespace netdutils {
// Wrapper around a combination of Status and application value type.
// T may be any copyable or movable type.
template <typename T>
class [[nodiscard]] StatusOr {
// Constructs a new StatusOr with status::undefined status.
// This is marked 'explicit' to try to catch cases like 'return {};',
// where people think StatusOr<std::vector<int>> will be initialized
// with an empty vector, instead of a status::undefined.
explicit StatusOr() = default;
// Implicit copy constructor and construction from T.
// NOLINTNEXTLINE(google-explicit-constructor)
StatusOr(Status status) : mStatus(std::move(status)) { assert(!isOk(mStatus)); }
// Implicit construction from T. It is convenient and sensible to be able
// to do 'return T()' when the return type is StatusOr<T>.
// NOLINTNEXTLINE(google-explicit-constructor)
StatusOr(const T& value) : mStatus(status::ok), mValue(value) {}
// NOLINTNEXTLINE(google-explicit-constructor)
StatusOr(T&& value) : mStatus(status::ok), mValue(std::move(value)) {}
// Move constructor ok (if T supports move)
StatusOr(StatusOr&&) noexcept = default;
// Move assignment ok (if T supports move)
StatusOr& operator=(StatusOr&&) noexcept = default;
// Copy constructor ok (if T supports copy)
StatusOr(const StatusOr&) = default;
// Copy assignment ok (if T supports copy)
StatusOr& operator=(const StatusOr&) = default;
// Returns a const reference to wrapped type.
// It is an error to call value() when !isOk(status())
const T& value() const & { return mValue; }
const T&& value() const && { return mValue; }
// Returns an rvalue reference to wrapped type
// It is an error to call value() when !isOk(status())
// If T is expensive to copy but supports efficient move, it can be moved
// out of a StatusOr as follows:
// T value = std::move(statusor).value();
T& value() & { return mValue; }
T&& value() && { return mValue; }
// Returns the Status object assigned at construction time.
const Status status() const { return mStatus; }
// Explicitly ignores the Status without triggering [[nodiscard]] errors.
void ignoreError() const {}
// Implicit cast to Status.
// NOLINTNEXTLINE(google-explicit-constructor)
operator Status() const { return status(); }
Status mStatus = status::undefined;
T mValue;
template <typename T>
inline std::ostream& operator<<(std::ostream& os, const StatusOr<T>& s) {
return os << "StatusOr[status: " << s.status() << "]";
#define ASSIGN_OR_RETURN_IMPL(tmp, lhs, stmt) \
auto tmp = (stmt); \
lhs = std::move(tmp.value());
#define ASSIGN_OR_RETURN_CONCAT(line, lhs, stmt) \
ASSIGN_OR_RETURN_IMPL(__CONCAT(_status_or_, line), lhs, stmt)
// Macro to allow exception-like handling of error return values.
// If the evaluation of stmt results in an error, return that error
// from the current function. Otherwise, assign the result to lhs.
// This macro supports both move and copy assignment operators. lhs
// may be either a new local variable or an existing non-const
// variable accessible in the current scope.
// Example usage:
// StatusOr<MyType> foo() { ... }
// ASSIGN_OR_RETURN(auto myVar, foo());
// ASSIGN_OR_RETURN(myExistingVar, foo());
// ASSIGN_OR_RETURN(myMemberVar, foo());
#define ASSIGN_OR_RETURN(lhs, stmt) ASSIGN_OR_RETURN_CONCAT(__LINE__, lhs, stmt)
} // namespace netdutils
} // namespace android