Down-integrate from internal code base.

[ci skip]

Change-Id: I9391c09640e0b0b2b21c45a97a1fc91814d95c5d

1 files changed, 259 insertions, 0 deletions

diff --git a/src/google/protobuf/stubs/statusor.h b/src/google/protobuf/stubs/statusor.h
new file mode 100644
index 00000000..9495107e
--- /dev/null
+++ b/src/google/protobuf/stubs/statusor.h
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+// 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 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.value_) {
+}
+
+template<typename T>
+template<typename U>
+inline StatusOr<T>& StatusOr<T>::operator=(const StatusOr<U>& other) {
+  status_ = other.status_;
+  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_