chromium/third_party/openscreen/src/platform/base/error.h

// Copyright 2018 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef PLATFORM_BASE_ERROR_H_
#define PLATFORM_BASE_ERROR_H_

#include <cassert>
#include <ostream>
#include <string>
#include <utility>

#include "platform/base/macros.h"

namespace openscreen {

// Represents an error returned by an OSP library operation.  An error has a
// code and an optional message.
class Error { … };

std::string ToString(openscreen::Error::Code code);
std::ostream& operator<<(std::ostream& os, const Error::Code& code);
std::ostream& operator<<(std::ostream& out, const Error& error);

// A convenience function to return a single value from a function that can
// return a value or an error.  For normal results, construct with a ValueType*
// (ErrorOr takes ownership) and the Error will be kNone with an empty message.
// For Error results, construct with an error code and value.
//
// Example:
//
// ErrorOr<Bar> Foo::DoSomething() {
//   if (success) {
//     return Bar();
//   } else {
//     return Error(kBadThingHappened, "No can do");
//   }
// }
//
// TODO(mfoltz): Add support for type conversions.
template <typename ValueType>
class ErrorOr { … };

// Define comparison operators using SFINAE.
template <typename ValueType>
bool operator<(const ErrorOr<ValueType>& lhs, const ErrorOr<ValueType>& rhs) { … }

template <typename ValueType>
bool operator>(const ErrorOr<ValueType>& lhs, const ErrorOr<ValueType>& rhs) { … }

template <typename ValueType>
bool operator<=(const ErrorOr<ValueType>& lhs, const ErrorOr<ValueType>& rhs) { … }

template <typename ValueType>
bool operator>=(const ErrorOr<ValueType>& lhs, const ErrorOr<ValueType>& rhs) { … }

template <typename ValueType>
bool operator==(const ErrorOr<ValueType>& lhs, const ErrorOr<ValueType>& rhs) { … }

template <typename ValueType>
bool operator!=(const ErrorOr<ValueType>& lhs, const ErrorOr<ValueType>& rhs) { … }

}  // namespace openscreen

#endif  // PLATFORM_BASE_ERROR_H_