// Protocol Buffers - Google's data interchange format
// Copyright 2008 Google Inc. All rights reserved.
// https://developers.google.com/protocol-buffers/
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
//
// * Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
// * Redistributions in binary form must reproduce the above
// copyright notice, this list of conditions and the following disclaimer
// in the documentation and/or other materials provided with the
// distribution.
// * Neither the name of Google Inc. nor the names of its
// contributors may be used to endorse or promote products derived from
// this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
// StatusOr<T> is the union of a Status object and a T
// object. StatusOr models the concept of an object that is either a
// usable value, or an error Status explaining why such a value is
// not present. To this end, StatusOr<T> does not allow its Status
// value to be Status::OK. Further, StatusOr<T*> does not allow the
// contained pointer to be NULL.
//
// The primary use-case for StatusOr<T> is as the return value of a
// function which may fail.
//
// Example client usage for a StatusOr<T>, where T is not a pointer:
//
// StatusOr<float> result = DoBigCalculationThatCouldFail();
// if (result.ok()) {
// float answer = result.ValueOrDie();
// printf("Big calculation yielded: %f", answer);
// } else {
// LOG(ERROR) << result.status();
// }
//
// Example client usage for a StatusOr<T*>:
//
// StatusOr<Foo*> result = FooFactory::MakeNewFoo(arg);
// if (result.ok()) {
// std::unique_ptr<Foo> foo(result.ValueOrDie());
// foo->DoSomethingCool();
// } else {
// LOG(ERROR) << result.status();
// }
//
// Example client usage for a StatusOr<std::unique_ptr<T>>:
//
// StatusOr<std::unique_ptr<Foo>> result = FooFactory::MakeNewFoo(arg);
// if (result.ok()) {
// std::unique_ptr<Foo> foo = result.ConsumeValueOrDie();
// foo->DoSomethingCool();
// } else {
// LOG(ERROR) << result.status();
// }
//
// Example factory implementation returning StatusOr<T*>:
//
// StatusOr<Foo*> FooFactory::MakeNewFoo(int arg) {
// if (arg <= 0) {
// return ::util::Status(::util::error::INVALID_ARGUMENT,
// "Arg must be positive");
// } else {
// return new Foo(arg);
// }
// }
//
#ifndef GOOGLE_PROTOBUF_STUBS_STATUSOR_H_
#define GOOGLE_PROTOBUF_STUBS_STATUSOR_H_
#include <new>
#include <string>
#include <utility>
#include <google/protobuf/stubs/status.h>
namespace google {
namespace protobuf {
namespace util {
template<typename T>
class StatusOr {
template<typename U> friend class StatusOr;
public:
// Construct a new StatusOr with Status::UNKNOWN status
StatusOr();
// Construct a new StatusOr with the given non-ok status. After calling
// this constructor, calls to ValueOrDie() will CHECK-fail.
//
// NOTE: Not explicit - we want to use StatusOr<T> as a return
// value, so it is convenient and sensible to be able to do 'return
// Status()' when the return type is StatusOr<T>.
//
// REQUIRES: status != Status::OK. This requirement is DCHECKed.
// In optimized builds, passing Status::OK here will have the effect
// of passing PosixErrorSpace::EINVAL as a fallback.
StatusOr(const Status& status); // NOLINT
// Construct a new StatusOr with the given value. If T is a plain pointer,
// value must not be NULL. After calling this constructor, calls to
// ValueOrDie() will succeed, and calls to status() will return OK.
//
// NOTE: Not explicit - we want to use StatusOr<T> as a return type
// so it is convenient and sensible to be able to do 'return T()'
// when when the return type is StatusOr<T>.
//
// REQUIRES: if T is a plain pointer, value != NULL. This requirement is
// DCHECKed. In optimized builds, passing a NULL pointer here will have
// the effect of passing PosixErrorSpace::EINVAL as a fallback.
StatusOr(const T& value); // NOLINT
// Copy constructor.
StatusOr(const StatusOr& other);
// Conversion copy constructor, T must be copy constructible from U
template<typename U>
StatusOr(const StatusOr<U>& other);
// Assignment operator.
StatusOr& operator=(const StatusOr& other);
// Conversion assignment operator, T must be assignable from U
template<typename U>
StatusOr& operator=(const StatusOr<U>& other);
// Returns a reference to our status. If this contains a T, then
// returns Status::OK.
const Status& status() const;
// Returns this->status().ok()
bool ok() const;
// Returns a reference to our current value, or CHECK-fails if !this->ok().
// If you need to initialize a T object from the stored value,
// ConsumeValueOrDie() may be more efficient.
const T& ValueOrDie() const;
private:
Status status_;
T value_;
};
////////////////////////////////////////////////////////////////////////////////
// Implementation details for StatusOr<T>
namespace internal {
class LIBPROTOBUF_EXPORT StatusOrHelper {
public:
// Move type-agnostic error handling to the .cc.
static void Crash(const util::Status& status);
// Customized behavior for StatusOr<T> vs. StatusOr<T*>
template<typename T>
struct Specialize;
};
template<typename T>
struct StatusOrHelper::Specialize {
// For non-pointer T, a reference can never be NULL.
static inline bool IsValueNull(const T& t) { return false; }
};
template<typename T>
struct StatusOrHelper::Specialize<T*> {
static inline bool IsValueNull(const T* t) { return t == NULL; }
};
} // namespace internal
template<typename T>
inline StatusOr<T>::StatusOr()
: status_(util::Status::UNKNOWN) {
}
template<typename T>
inline StatusOr<T>::StatusOr(const Status& status) {
if (status.ok()) {
status_ = Status(error::INTERNAL, "Status::OK is not a valid argument.");
} else {
status_ = status;
}
}
template<typename T>
inline StatusOr<T>::StatusOr(const T& value) {
if (internal::StatusOrHelper::Specialize<T>::IsValueNull(value)) {
status_ = Status(error::INTERNAL, "NULL is not a vaild argument.");
} else {
status_ = Status::OK;
value_ = value;
}
}
template<typename T>
inline StatusOr<T>::StatusOr(const StatusOr<T>& other)
: status_(other.status_), value_(other.value_) {
}
template<typename T>
inline StatusOr<T>& StatusOr<T>::operator=(const StatusOr<T>& other) {
status_ = other.status_;
value_ = other.value_;
return *this;
}
template<typename T>
template<typename U>
inline StatusOr<T>::StatusOr(const StatusOr<U>& other)
: status_(other.status_), value_(other.status_.ok() ? other.value_ : T()) {
}
template<typename T>
template<typename U>
inline StatusOr<T>& StatusOr<T>::operator=(const StatusOr<U>& other) {
status_ = other.status_;
if (status_.ok()) value_ = other.value_;
return *this;
}
template<typename T>
inline const Status& StatusOr<T>::status() const {
return status_;
}
template<typename T>
inline bool StatusOr<T>::ok() const {
return status().ok();
}
template<typename T>
inline const T& StatusOr<T>::ValueOrDie() const {
if (!status_.ok()) {
internal::StatusOrHelper::Crash(status_);
}
return value_;
}
} // namespace util
} // namespace protobuf
} // namespace google
#endif // GOOGLE_PROTOBUF_STUBS_STATUSOR_H_
