statusor.h

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// Copyright (c) 2017, The Regents of the University of California
// All rights reserved.
//
// 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 the University of California 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 REGENTS OF THE UNIVERSITY OF CALIFORNIA
// 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 UTIL_STATUSOR_H_
#define UTIL_STATUSOR_H_

#include <assert.h>

#include <new>
#include <string>
#include <utility>

#include "util/status.h"

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);

  // Rvalue-reference overloads of the other constructors and assignment
  // operators, to support move-only types and avoid unnecessary copying.
  StatusOr(T&& value);  // NOLINT

  // Move conversion operator to avoid unecessary copy.
  // T must be assignable from U.
  // Not marked with explicit so the implicit conversion can happen.
  template <typename U>
  StatusOr(StatusOr<U>&& other);  // NOLINT

  // Move assignment opeartor to avoid unnecessary copy.
  // T must be assignable from U
  template <typename U>
  StatusOr& operator=(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;

  // Returns our current value, requires this->ok(). Use this if
  // you would otherwise want to say std::move(s.ValueOrDie()), for example
  // if you need to initialize a T object from the stored value and you don't
  // need subsequent access to the stored value. It uses T's move constructor,
  // if it has one, so it will work with move-only types, and will often be
  // more efficient than ValueOrDie, but may leave the stored value
  // in an arbitrary valid state.
  T ConsumeValueOrDie();

 private:
  void CheckValueNotNull(const T& value);

  template <typename U>
  struct IsNull {
    // For non-pointer U, a reference can never be NULL.
    static inline bool IsValueNull(const U& t) { return false; }
  };

  template <typename U>
  struct IsNull<U*> {
    static inline bool IsValueNull(const U* t) { return t == NULL; }
  };

  Status status_;
  T value_;
};

// Implementation details for StatusOr<T>

namespace internal {

class 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_;
}

// Adpoted from tensorflow/stream_executor/lib/statusor.h

template <typename T>
inline StatusOr<T>::StatusOr(T&& value)
    : status_() {
  CheckValueNotNull(value);
  value_ = std::move(value);
}

template <typename T>
inline T StatusOr<T>::ConsumeValueOrDie() {
  if (!status_.ok()) {
    internal::StatusOrHelper::Crash(status_);
  }
  return std::move(value_);
}

template <typename T>
template <typename U>
inline StatusOr<T>::StatusOr(StatusOr<U>&& other)  // NOLINT
    : status_(std::move(other.status_)),
      value_(std::move(other.value_)) {}

// Move assignment opeartor to avoid unnecessary copy.
// T must be assignable from U
template <typename T>
template <typename U>
inline StatusOr<T>& StatusOr<T>::operator=(StatusOr<U>&& other) {
  status_ = std::move(other.status_);
  value_ = std::move(other.value_);
  return *this;
}

template <typename T>
inline void StatusOr<T>::CheckValueNotNull(const T& value) {
  assert(!IsNull<T>::IsValueNull(value));
  if (IsNull<T>::IsValueNull(value)) {
    status_ =
        Status(error::INTERNAL,
               "NULL is not a valid constructor argument to StatusOr<T*>");
  }
}

}  // namespace util

#endif  // UTIL_STATUSOR_H_


// 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.


// Adpoted from tensorflow/stream_executor/lib/statusor.h
// Copyright 2015 Google Inc. All Rights Reserved.
// 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
//     http://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.