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authorGravatar Abseil Team <absl-team@google.com>2020-09-18 15:55:15 -0700
committerGravatar Derek Mauro <dmauro@google.com>2020-09-24 13:47:15 -0400
commitb56cbdd23834a65682c0b46f367f8679e83bc894 (patch)
treedacab9a64dd1a9e9668737e511d1a5420ff96001 /absl/status/statusor.h
parentb832dce8489ef7b6231384909fd9b68d5a5ff2b7 (diff)
Abseil LTS 2020092320200923
What's New: * `absl::StatusOr<T>` has been released. See our [blog post](https://abseil.io/blog/2020-091021-status) for more information. * Abseil Flags reflection interfaces have been released. * Abseil Flags memory usage has been significantly optimized. * Abseil now supports a "hardened" build mode. This build mode enables runtime checks that guard against programming errors that may lead to security vulnerabilities. Notable Fixes: * Sanitizer dynamic annotations like `AnnotateRWLockCreate` that are also defined by the compiler sanitizer implementation are no longer also defined by Abseil. * Sanitizer macros are now prefixed with `ABSL_` to avoid naming collisions. * Sanitizer usage is now automatically detected and no longer requires macros like `ADDRESS_SANITIZER` to be defined on the command line. Breaking Changes: * Abseil no longer contains a `dynamic_annotations` library. Users using a supported build system (Bazel or CMake) are unaffected by this, but users manually specifying link libraries may get an error about a missing linker input. Baseline: 7680a5f8efe32de4753baadbd63e74e59d95bac1 Cherry picks: None
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+// Copyright 2020 The Abseil Authors.
+//
+// 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
+//
+// https://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.
+//
+// -----------------------------------------------------------------------------
+// File: statusor.h
+// -----------------------------------------------------------------------------
+//
+// An `absl::StatusOr<T>` represents a union of an `absl::Status` object
+// and an object of type `T`. The `absl::StatusOr<T>` will either contain an
+// object of type `T` (indicating a successful operation), or an error (of type
+// `absl::Status`) explaining why such a value is not present.
+//
+// In general, check the success of an operation returning an
+// `absl::StatusOr<T>` like you would an `absl::Status` by using the `ok()`
+// member function.
+//
+// Example:
+//
+// StatusOr<Foo> result = Calculation();
+// if (result.ok()) {
+// result->DoSomethingCool();
+// } else {
+// LOG(ERROR) << result.status();
+// }
+#ifndef ABSL_STATUS_STATUSOR_H_
+#define ABSL_STATUS_STATUSOR_H_
+
+#include <exception>
+#include <initializer_list>
+#include <new>
+#include <string>
+#include <type_traits>
+#include <utility>
+
+#include "absl/base/attributes.h"
+#include "absl/meta/type_traits.h"
+#include "absl/status/internal/statusor_internal.h"
+#include "absl/status/status.h"
+#include "absl/types/variant.h"
+#include "absl/utility/utility.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+
+// BadStatusOrAccess
+//
+// This class defines the type of object to throw (if exceptions are enabled),
+// when accessing the value of an `absl::StatusOr<T>` object that does not
+// contain a value. This behavior is analogous to that of
+// `std::bad_optional_access` in the case of accessing an invalid
+// `std::optional` value.
+//
+// Example:
+//
+// try {
+// absl::StatusOr<int> v = FetchInt();
+// DoWork(v.value()); // Accessing value() when not "OK" may throw
+// } catch (absl::BadStatusOrAccess& ex) {
+// LOG(ERROR) << ex.status();
+// }
+class BadStatusOrAccess : public std::exception {
+ public:
+ explicit BadStatusOrAccess(absl::Status status);
+ ~BadStatusOrAccess() override;
+
+ // BadStatusOrAccess::what()
+ //
+ // Returns the associated explanatory string of the `absl::StatusOr<T>`
+ // object's error code. This function only returns the string literal "Bad
+ // StatusOr Access" for cases when evaluating general exceptions.
+ //
+ // The pointer of this string is guaranteed to be valid until any non-const
+ // function is invoked on the exception object.
+ const char* what() const noexcept override;
+
+ // BadStatusOrAccess::status()
+ //
+ // Returns the associated `absl::Status` of the `absl::StatusOr<T>` object's
+ // error.
+ const absl::Status& status() const;
+
+ private:
+ absl::Status status_;
+};
+
+// Returned StatusOr objects may not be ignored.
+template <typename T>
+class ABSL_MUST_USE_RESULT StatusOr;
+
+// absl::StatusOr<T>
+//
+// The `absl::StatusOr<T>` class template is a union of an `absl::Status` object
+// and an object of type `T`. The `absl::StatusOr<T>` models an object that is
+// either a usable object, or an error (of type `absl::Status`) explaining why
+// such an object is not present. An `absl::StatusOr<T>` is typically the return
+// value of a function which may fail.
+//
+// An `absl::StatusOr<T>` can never hold an "OK" status (an
+// `absl::StatusCode::kOk` value); instead, the presence of an object of type
+// `T` indicates success. Instead of checking for a `kOk` value, use the
+// `absl::StatusOr<T>::ok()` member function. (It is for this reason, and code
+// readability, that using the `ok()` function is preferred for `absl::Status`
+// as well.)
+//
+// Example:
+//
+// StatusOr<Foo> result = DoBigCalculationThatCouldFail();
+// if (result.ok()) {
+// result->DoSomethingCool();
+// } else {
+// LOG(ERROR) << result.status();
+// }
+//
+// Accessing the object held by an `absl::StatusOr<T>` should be performed via
+// `operator*` or `operator->`, after a call to `ok()` confirms that the
+// `absl::StatusOr<T>` holds an object of type `T`:
+//
+// Example:
+//
+// absl::StatusOr<int> i = GetCount();
+// if (foo.ok()) {
+// updated_total += *i
+// }
+//
+// NOTE: using `absl::StatusOr<T>::value()` when no valid value is present will
+// throw an exception if exceptions are enabled or terminate the process when
+// execeptions are not enabled.
+//
+// Example:
+//
+// StatusOr<Foo> result = DoBigCalculationThatCouldFail();
+// const Foo& foo = result.value(); // Crash/exception if no value present
+// foo.DoSomethingCool();
+//
+// A `absl::StatusOr<T*>` can be constructed from a null pointer like any other
+// pointer value, and the result will be that `ok()` returns `true` and
+// `value()` returns `nullptr`. Checking the value of pointer in an
+// `absl::StatusOr<T>` generally requires a bit more care, to ensure both that a
+// value is present and that value is not null:
+//
+// StatusOr<std::unique_ptr<Foo>> result = FooFactory::MakeNewFoo(arg);
+// if (!result.ok()) {
+// LOG(ERROR) << result.status();
+// } else if (*result == nullptr) {
+// LOG(ERROR) << "Unexpected null pointer";
+// } else {
+// (*result)->DoSomethingCool();
+// }
+//
+// Example factory implementation returning StatusOr<T>:
+//
+// StatusOr<Foo> FooFactory::MakeFoo(int arg) {
+// if (arg <= 0) {
+// return absl::Status(absl::StatusCode::kInvalidArgument,
+// "Arg must be positive");
+// }
+// return Foo(arg);
+// }
+template <typename T>
+class StatusOr : private internal_statusor::StatusOrData<T>,
+ private internal_statusor::CopyCtorBase<T>,
+ private internal_statusor::MoveCtorBase<T>,
+ private internal_statusor::CopyAssignBase<T>,
+ private internal_statusor::MoveAssignBase<T> {
+ template <typename U>
+ friend class StatusOr;
+
+ typedef internal_statusor::StatusOrData<T> Base;
+
+ public:
+ // StatusOr<T>::value_type
+ //
+ // This instance data provides a generic `value_type` member for use within
+ // generic programming. This usage is analogous to that of
+ // `optional::value_type` in the case of `std::optional`.
+ typedef T value_type;
+
+ // Constructors
+
+ // Constructs a new `absl::StatusOr` with an `absl::StatusCode::kUnknown`
+ // status. This constructor is marked 'explicit' to prevent usages in return
+ // values such as 'return {};', under the misconception that
+ // `absl::StatusOr<std::vector<int>>` will be initialized with an empty
+ // vector, instead of an `absl::StatusCode::kUnknown` error code.
+ explicit StatusOr();
+
+ // `StatusOr<T>` is copy constructible if `T` is copy constructible.
+ StatusOr(const StatusOr&) = default;
+ // `StatusOr<T>` is copy assignable if `T` is copy constructible and copy
+ // assignable.
+ StatusOr& operator=(const StatusOr&) = default;
+
+ // `StatusOr<T>` is move constructible if `T` is move constructible.
+ StatusOr(StatusOr&&) = default;
+ // `StatusOr<T>` is moveAssignable if `T` is move constructible and move
+ // assignable.
+ StatusOr& operator=(StatusOr&&) = default;
+
+ // Converting Constructors
+
+ // Constructs a new `absl::StatusOr<T>` from an `absl::StatusOr<U>`, when `T`
+ // is constructible from `U`. To avoid ambiguity, these constructors are
+ // disabled if `T` is also constructible from `StatusOr<U>.`. This constructor
+ // is explicit if and only if the corresponding construction of `T` from `U`
+ // is explicit. (This constructor inherits its explicitness from the
+ // underlying constructor.)
+ template <
+ typename U,
+ absl::enable_if_t<
+ absl::conjunction<
+ absl::negation<std::is_same<T, U>>,
+ std::is_constructible<T, const U&>,
+ std::is_convertible<const U&, T>,
+ absl::negation<
+ internal_statusor::IsConstructibleOrConvertibleFromStatusOr<
+ T, U>>>::value,
+ int> = 0>
+ StatusOr(const StatusOr<U>& other) // NOLINT
+ : Base(static_cast<const typename StatusOr<U>::Base&>(other)) {}
+ template <
+ typename U,
+ absl::enable_if_t<
+ absl::conjunction<
+ absl::negation<std::is_same<T, U>>,
+ std::is_constructible<T, const U&>,
+ absl::negation<std::is_convertible<const U&, T>>,
+ absl::negation<
+ internal_statusor::IsConstructibleOrConvertibleFromStatusOr<
+ T, U>>>::value,
+ int> = 0>
+ explicit StatusOr(const StatusOr<U>& other)
+ : Base(static_cast<const typename StatusOr<U>::Base&>(other)) {}
+
+ template <
+ typename U,
+ absl::enable_if_t<
+ absl::conjunction<
+ absl::negation<std::is_same<T, U>>, std::is_constructible<T, U&&>,
+ std::is_convertible<U&&, T>,
+ absl::negation<
+ internal_statusor::IsConstructibleOrConvertibleFromStatusOr<
+ T, U>>>::value,
+ int> = 0>
+ StatusOr(StatusOr<U>&& other) // NOLINT
+ : Base(static_cast<typename StatusOr<U>::Base&&>(other)) {}
+ template <
+ typename U,
+ absl::enable_if_t<
+ absl::conjunction<
+ absl::negation<std::is_same<T, U>>, std::is_constructible<T, U&&>,
+ absl::negation<std::is_convertible<U&&, T>>,
+ absl::negation<
+ internal_statusor::IsConstructibleOrConvertibleFromStatusOr<
+ T, U>>>::value,
+ int> = 0>
+ explicit StatusOr(StatusOr<U>&& other)
+ : Base(static_cast<typename StatusOr<U>::Base&&>(other)) {}
+
+ // Converting Assignment Operators
+
+ // Creates an `absl::StatusOr<T>` through assignment from an
+ // `absl::StatusOr<U>` when:
+ //
+ // * Both `absl::StatusOr<T>` and `absl::StatusOr<U>` are OK by assigning
+ // `U` to `T` directly.
+ // * `absl::StatusOr<T>` is OK and `absl::StatusOr<U>` contains an error
+ // code by destroying `absl::StatusOr<T>`'s value and assigning from
+ // `absl::StatusOr<U>'
+ // * `absl::StatusOr<T>` contains an error code and `absl::StatusOr<U>` is
+ // OK by directly initializing `T` from `U`.
+ // * Both `absl::StatusOr<T>` and `absl::StatusOr<U>` contain an error
+ // code by assigning the `Status` in `absl::StatusOr<U>` to
+ // `absl::StatusOr<T>`
+ //
+ // These overloads only apply if `absl::StatusOr<T>` is constructible and
+ // assignable from `absl::StatusOr<U>` and `StatusOr<T>` cannot be directly
+ // assigned from `StatusOr<U>`.
+ template <
+ typename U,
+ absl::enable_if_t<
+ absl::conjunction<
+ absl::negation<std::is_same<T, U>>,
+ std::is_constructible<T, const U&>,
+ std::is_assignable<T, const U&>,
+ absl::negation<
+ internal_statusor::
+ IsConstructibleOrConvertibleOrAssignableFromStatusOr<
+ T, U>>>::value,
+ int> = 0>
+ StatusOr& operator=(const StatusOr<U>& other) {
+ this->Assign(other);
+ return *this;
+ }
+ template <
+ typename U,
+ absl::enable_if_t<
+ absl::conjunction<
+ absl::negation<std::is_same<T, U>>, std::is_constructible<T, U&&>,
+ std::is_assignable<T, U&&>,
+ absl::negation<
+ internal_statusor::
+ IsConstructibleOrConvertibleOrAssignableFromStatusOr<
+ T, U>>>::value,
+ int> = 0>
+ StatusOr& operator=(StatusOr<U>&& other) {
+ this->Assign(std::move(other));
+ return *this;
+ }
+
+ // Constructs a new `absl::StatusOr<T>` with a non-ok status. After calling
+ // this constructor, `this->ok()` will be `false` and calls to `value()` will
+ // crash, or produce an exception if exceptions are enabled.
+ //
+ // The constructor also takes any type `U` that is convertible to
+ // `absl::Status`. This constructor is explicit if an only if `U` is not of
+ // type `absl::Status` and the conversion from `U` to `Status` is explicit.
+ //
+ // REQUIRES: !Status(std::forward<U>(v)).ok(). This requirement is DCHECKed.
+ // In optimized builds, passing absl::OkStatus() here will have the effect
+ // of passing absl::StatusCode::kInternal as a fallback.
+ template <
+ typename U = absl::Status,
+ absl::enable_if_t<
+ absl::conjunction<
+ std::is_convertible<U&&, absl::Status>,
+ std::is_constructible<absl::Status, U&&>,
+ absl::negation<std::is_same<absl::decay_t<U>, absl::StatusOr<T>>>,
+ absl::negation<std::is_same<absl::decay_t<U>, T>>,
+ absl::negation<std::is_same<absl::decay_t<U>, absl::in_place_t>>,
+ absl::negation<internal_statusor::HasConversionOperatorToStatusOr<
+ T, U&&>>>::value,
+ int> = 0>
+ StatusOr(U&& v) : Base(std::forward<U>(v)) {}
+
+ template <
+ typename U = absl::Status,
+ absl::enable_if_t<
+ absl::conjunction<
+ absl::negation<std::is_convertible<U&&, absl::Status>>,
+ std::is_constructible<absl::Status, U&&>,
+ absl::negation<std::is_same<absl::decay_t<U>, absl::StatusOr<T>>>,
+ absl::negation<std::is_same<absl::decay_t<U>, T>>,
+ absl::negation<std::is_same<absl::decay_t<U>, absl::in_place_t>>,
+ absl::negation<internal_statusor::HasConversionOperatorToStatusOr<
+ T, U&&>>>::value,
+ int> = 0>
+ explicit StatusOr(U&& v) : Base(std::forward<U>(v)) {}
+
+ template <
+ typename U = absl::Status,
+ absl::enable_if_t<
+ absl::conjunction<
+ std::is_convertible<U&&, absl::Status>,
+ std::is_constructible<absl::Status, U&&>,
+ absl::negation<std::is_same<absl::decay_t<U>, absl::StatusOr<T>>>,
+ absl::negation<std::is_same<absl::decay_t<U>, T>>,
+ absl::negation<std::is_same<absl::decay_t<U>, absl::in_place_t>>,
+ absl::negation<internal_statusor::HasConversionOperatorToStatusOr<
+ T, U&&>>>::value,
+ int> = 0>
+ StatusOr& operator=(U&& v) {
+ this->AssignStatus(std::forward<U>(v));
+ return *this;
+ }
+
+ // Perfect-forwarding value assignment operator.
+
+ // If `*this` contains a `T` value before the call, the contained value is
+ // assigned from `std::forward<U>(v)`; Otherwise, it is directly-initialized
+ // from `std::forward<U>(v)`.
+ // This function does not participate in overload unless:
+ // 1. `std::is_constructible_v<T, U>` is true,
+ // 2. `std::is_assignable_v<T&, U>` is true.
+ // 3. `std::is_same_v<StatusOr<T>, std::remove_cvref_t<U>>` is false.
+ // 4. Assigning `U` to `T` is not ambiguous:
+ // If `U` is `StatusOr<V>` and `T` is constructible and assignable from
+ // both `StatusOr<V>` and `V`, the assignment is considered bug-prone and
+ // ambiguous thus will fail to compile. For example:
+ // StatusOr<bool> s1 = true; // s1.ok() && *s1 == true
+ // StatusOr<bool> s2 = false; // s2.ok() && *s2 == false
+ // s1 = s2; // ambiguous, `s1 = *s2` or `s1 = bool(s2)`?
+ template <
+ typename U = T,
+ typename = typename std::enable_if<absl::conjunction<
+ std::is_constructible<T, U&&>, std::is_assignable<T&, U&&>,
+ absl::disjunction<
+ std::is_same<absl::remove_cv_t<absl::remove_reference_t<U>>, T>,
+ absl::conjunction<
+ absl::negation<std::is_convertible<U&&, absl::Status>>,
+ absl::negation<internal_statusor::
+ HasConversionOperatorToStatusOr<T, U&&>>>>,
+ internal_statusor::IsForwardingAssignmentValid<T, U&&>>::value>::type>
+ StatusOr& operator=(U&& v) {
+ this->Assign(std::forward<U>(v));
+ return *this;
+ }
+
+ // Constructs the inner value `T` in-place using the provided args, using the
+ // `T(args...)` constructor.
+ template <typename... Args>
+ explicit StatusOr(absl::in_place_t, Args&&... args);
+ template <typename U, typename... Args>
+ explicit StatusOr(absl::in_place_t, std::initializer_list<U> ilist,
+ Args&&... args);
+
+ // Constructs the inner value `T` in-place using the provided args, using the
+ // `T(U)` (direct-initialization) constructor. This constructor is only valid
+ // if `T` can be constructed from a `U`. Can accept move or copy constructors.
+ //
+ // This constructor is explicit if `U` is not convertible to `T`. To avoid
+ // ambiguity, this constuctor is disabled if `U` is a `StatusOr<J>`, where `J`
+ // is convertible to `T`.
+ template <
+ typename U = T,
+ absl::enable_if_t<
+ absl::conjunction<
+ internal_statusor::IsDirectInitializationValid<T, U&&>,
+ std::is_constructible<T, U&&>, std::is_convertible<U&&, T>,
+ absl::disjunction<
+ std::is_same<absl::remove_cv_t<absl::remove_reference_t<U>>,
+ T>,
+ absl::conjunction<
+ absl::negation<std::is_convertible<U&&, absl::Status>>,
+ absl::negation<
+ internal_statusor::HasConversionOperatorToStatusOr<
+ T, U&&>>>>>::value,
+ int> = 0>
+ StatusOr(U&& u) // NOLINT
+ : StatusOr(absl::in_place, std::forward<U>(u)) {
+ }
+
+ template <
+ typename U = T,
+ absl::enable_if_t<
+ absl::conjunction<
+ internal_statusor::IsDirectInitializationValid<T, U&&>,
+ absl::disjunction<
+ std::is_same<absl::remove_cv_t<absl::remove_reference_t<U>>,
+ T>,
+ absl::conjunction<
+ absl::negation<std::is_constructible<absl::Status, U&&>>,
+ absl::negation<
+ internal_statusor::HasConversionOperatorToStatusOr<
+ T, U&&>>>>,
+ std::is_constructible<T, U&&>,
+ absl::negation<std::is_convertible<U&&, T>>>::value,
+ int> = 0>
+ explicit StatusOr(U&& u) // NOLINT
+ : StatusOr(absl::in_place, std::forward<U>(u)) {
+ }
+
+ // StatusOr<T>::ok()
+ //
+ // Returns whether or not this `absl::StatusOr<T>` holds a `T` value. This
+ // member function is analagous to `absl::Status::ok()` and should be used
+ // similarly to check the status of return values.
+ //
+ // Example:
+ //
+ // StatusOr<Foo> result = DoBigCalculationThatCouldFail();
+ // if (result.ok()) {
+ // // Handle result
+ // else {
+ // // Handle error
+ // }
+ ABSL_MUST_USE_RESULT bool ok() const { return this->status_.ok(); }
+
+ // StatusOr<T>::status()
+ //
+ // Returns a reference to the current `absl::Status` contained within the
+ // `absl::StatusOr<T>`. If `absl::StatusOr<T>` contains a `T`, then this
+ // function returns `absl::OkStatus()`.
+ const Status& status() const &;
+ Status status() &&;
+
+ // StatusOr<T>::value()
+ //
+ // Returns a reference to the held value if `this->ok()`. Otherwise, throws
+ // `absl::BadStatusOrAccess` if exceptions are enabled, or is guaranteed to
+ // terminate the process if exceptions are disabled.
+ //
+ // If you have already checked the status using `this->ok()`, you probably
+ // want to use `operator*()` or `operator->()` to access the value instead of
+ // `value`.
+ //
+ // Note: for value types that are cheap to copy, prefer simple code:
+ //
+ // T value = statusor.value();
+ //
+ // Otherwise, if the value type is expensive to copy, but can be left
+ // in the StatusOr, simply assign to a reference:
+ //
+ // T& value = statusor.value(); // or `const T&`
+ //
+ // Otherwise, if the value type supports an efficient move, it can be
+ // used as follows:
+ //
+ // T value = std::move(statusor).value();
+ //
+ // The `std::move` on statusor instead of on the whole expression enables
+ // warnings about possible uses of the statusor object after the move.
+ const T& value() const&;
+ T& value() &;
+ const T&& value() const&&;
+ T&& value() &&;
+
+ // StatusOr<T>:: operator*()
+ //
+ // Returns a reference to the current value.
+ //
+ // REQUIRES: `this->ok() == true`, otherwise the behavior is undefined.
+ //
+ // Use `this->ok()` to verify that there is a current value within the
+ // `absl::StatusOr<T>`. Alternatively, see the `value()` member function for a
+ // similar API that guarantees crashing or throwing an exception if there is
+ // no current value.
+ const T& operator*() const&;
+ T& operator*() &;
+ const T&& operator*() const&&;
+ T&& operator*() &&;
+
+ // StatusOr<T>::operator->()
+ //
+ // Returns a pointer to the current value.
+ //
+ // REQUIRES: `this->ok() == true`, otherwise the behavior is undefined.
+ //
+ // Use `this->ok()` to verify that there is a current value.
+ const T* operator->() const;
+ T* operator->();
+
+ // StatusOr<T>::value_or()
+ //
+ // Returns the current value of `this->ok() == true`. Otherwise constructs a
+ // value using the provided `default_value`.
+ //
+ // Unlike `value`, this function returns by value, copying the current value
+ // if necessary. If the value type supports an efficient move, it can be used
+ // as follows:
+ //
+ // T value = std::move(statusor).value_or(def);
+ //
+ // Unlike with `value`, calling `std::move()` on the result of `value_or` will
+ // still trigger a copy.
+ template <typename U>
+ T value_or(U&& default_value) const&;
+ template <typename U>
+ T value_or(U&& default_value) &&;
+
+ // StatusOr<T>::IgnoreError()
+ //
+ // Ignores any errors. This method does nothing except potentially suppress
+ // complaints from any tools that are checking that errors are not dropped on
+ // the floor.
+ void IgnoreError() const;
+
+ // StatusOr<T>::emplace()
+ //
+ // Reconstructs the inner value T in-place using the provided args, using the
+ // T(args...) constructor. Returns reference to the reconstructed `T`.
+ template <typename... Args>
+ T& emplace(Args&&... args) {
+ if (ok()) {
+ this->Clear();
+ this->MakeValue(std::forward<Args>(args)...);
+ } else {
+ this->MakeValue(std::forward<Args>(args)...);
+ this->status_ = absl::OkStatus();
+ }
+ return this->data_;
+ }
+
+ template <
+ typename U, typename... Args,
+ absl::enable_if_t<
+ std::is_constructible<T, std::initializer_list<U>&, Args&&...>::value,
+ int> = 0>
+ T& emplace(std::initializer_list<U> ilist, Args&&... args) {
+ if (ok()) {
+ this->Clear();
+ this->MakeValue(ilist, std::forward<Args>(args)...);
+ } else {
+ this->MakeValue(ilist, std::forward<Args>(args)...);
+ this->status_ = absl::OkStatus();
+ }
+ return this->data_;
+ }
+
+ private:
+ using internal_statusor::StatusOrData<T>::Assign;
+ template <typename U>
+ void Assign(const absl::StatusOr<U>& other);
+ template <typename U>
+ void Assign(absl::StatusOr<U>&& other);
+};
+
+// operator==()
+//
+// This operator checks the equality of two `absl::StatusOr<T>` objects.
+template <typename T>
+bool operator==(const StatusOr<T>& lhs, const StatusOr<T>& rhs) {
+ if (lhs.ok() && rhs.ok()) return *lhs == *rhs;
+ return lhs.status() == rhs.status();
+}
+
+// operator!=()
+//
+// This operator checks the inequality of two `absl::StatusOr<T>` objects.
+template <typename T>
+bool operator!=(const StatusOr<T>& lhs, const StatusOr<T>& rhs) {
+ return !(lhs == rhs);
+}
+
+//------------------------------------------------------------------------------
+// Implementation details for StatusOr<T>
+//------------------------------------------------------------------------------
+
+// TODO(sbenza): avoid the string here completely.
+template <typename T>
+StatusOr<T>::StatusOr() : Base(Status(absl::StatusCode::kUnknown, "")) {}
+
+template <typename T>
+template <typename U>
+inline void StatusOr<T>::Assign(const StatusOr<U>& other) {
+ if (other.ok()) {
+ this->Assign(*other);
+ } else {
+ this->AssignStatus(other.status());
+ }
+}
+
+template <typename T>
+template <typename U>
+inline void StatusOr<T>::Assign(StatusOr<U>&& other) {
+ if (other.ok()) {
+ this->Assign(*std::move(other));
+ } else {
+ this->AssignStatus(std::move(other).status());
+ }
+}
+template <typename T>
+template <typename... Args>
+StatusOr<T>::StatusOr(absl::in_place_t, Args&&... args)
+ : Base(absl::in_place, std::forward<Args>(args)...) {}
+
+template <typename T>
+template <typename U, typename... Args>
+StatusOr<T>::StatusOr(absl::in_place_t, std::initializer_list<U> ilist,
+ Args&&... args)
+ : Base(absl::in_place, ilist, std::forward<Args>(args)...) {}
+
+template <typename T>
+const Status& StatusOr<T>::status() const & { return this->status_; }
+template <typename T>
+Status StatusOr<T>::status() && {
+ return ok() ? OkStatus() : std::move(this->status_);
+}
+
+template <typename T>
+const T& StatusOr<T>::value() const& {
+ if (!this->ok()) internal_statusor::ThrowBadStatusOrAccess(this->status_);
+ return this->data_;
+}
+
+template <typename T>
+T& StatusOr<T>::value() & {
+ if (!this->ok()) internal_statusor::ThrowBadStatusOrAccess(this->status_);
+ return this->data_;
+}
+
+template <typename T>
+const T&& StatusOr<T>::value() const&& {
+ if (!this->ok()) {
+ internal_statusor::ThrowBadStatusOrAccess(std::move(this->status_));
+ }
+ return std::move(this->data_);
+}
+
+template <typename T>
+T&& StatusOr<T>::value() && {
+ if (!this->ok()) {
+ internal_statusor::ThrowBadStatusOrAccess(std::move(this->status_));
+ }
+ return std::move(this->data_);
+}
+
+template <typename T>
+const T& StatusOr<T>::operator*() const& {
+ this->EnsureOk();
+ return this->data_;
+}
+
+template <typename T>
+T& StatusOr<T>::operator*() & {
+ this->EnsureOk();
+ return this->data_;
+}
+
+template <typename T>
+const T&& StatusOr<T>::operator*() const&& {
+ this->EnsureOk();
+ return std::move(this->data_);
+}
+
+template <typename T>
+T&& StatusOr<T>::operator*() && {
+ this->EnsureOk();
+ return std::move(this->data_);
+}
+
+template <typename T>
+const T* StatusOr<T>::operator->() const {
+ this->EnsureOk();
+ return &this->data_;
+}
+
+template <typename T>
+T* StatusOr<T>::operator->() {
+ this->EnsureOk();
+ return &this->data_;
+}
+
+template <typename T>
+template <typename U>
+T StatusOr<T>::value_or(U&& default_value) const& {
+ if (ok()) {
+ return this->data_;
+ }
+ return std::forward<U>(default_value);
+}
+
+template <typename T>
+template <typename U>
+T StatusOr<T>::value_or(U&& default_value) && {
+ if (ok()) {
+ return std::move(this->data_);
+ }
+ return std::forward<U>(default_value);
+}
+
+template <typename T>
+void StatusOr<T>::IgnoreError() const {
+ // no-op
+}
+
+ABSL_NAMESPACE_END
+} // namespace absl
+
+#endif // ABSL_STATUS_STATUSOR_H_