path: root/contrib/restricted/abseil-cpp-tstring/y_absl/status/statusor.h

// 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 `y_absl::StatusOr<T>` represents a union of an `y_absl::Status` object 
// and an object of type `T`. The `y_absl::StatusOr<T>` will either contain an 
// object of type `T` (indicating a successful operation), or an error (of type 
// `y_absl::Status`) explaining why such a value is not present. 
// 
// In general, check the success of an operation returning an 
// `y_absl::StatusOr<T>` like you would an `y_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 <util/generic/string.h> 
#include <type_traits> 
#include <utility> 
 
#include "y_absl/base/attributes.h" 
#include "y_absl/base/call_once.h"
#include "y_absl/meta/type_traits.h" 
#include "y_absl/status/internal/statusor_internal.h" 
#include "y_absl/status/status.h" 
#include "y_absl/types/variant.h" 
#include "y_absl/utility/utility.h" 
 
namespace y_absl { 
ABSL_NAMESPACE_BEGIN 
 
// BadStatusOrAccess 
// 
// This class defines the type of object to throw (if exceptions are enabled), 
// when accessing the value of an `y_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 { 
//   y_absl::StatusOr<int> v = FetchInt(); 
//   DoWork(v.value());  // Accessing value() when not "OK" may throw 
// } catch (y_absl::BadStatusOrAccess& ex) { 
//   LOG(ERROR) << ex.status(); 
// } 
class BadStatusOrAccess : public std::exception { 
 public: 
  explicit BadStatusOrAccess(y_absl::Status status); 
  ~BadStatusOrAccess() override = default;
 
  BadStatusOrAccess(const BadStatusOrAccess& other);
  BadStatusOrAccess& operator=(const BadStatusOrAccess& other);
  BadStatusOrAccess(BadStatusOrAccess&& other);
  BadStatusOrAccess& operator=(BadStatusOrAccess&& other);

  // BadStatusOrAccess::what() 
  // 
  // Returns the associated explanatory string of the `y_absl::StatusOr<T>` 
  // object's error code. This function contains information about the failing
  // status, but its exact formatting may change and should not be depended on.
  // 
  // 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 `y_absl::Status` of the `y_absl::StatusOr<T>` object's 
  // error. 
  const y_absl::Status& status() const; 
 
 private: 
  void InitWhat() const;

  y_absl::Status status_; 
  mutable y_absl::once_flag init_what_;
  mutable TString what_;
}; 
 
// Returned StatusOr objects may not be ignored. 
template <typename T> 
class ABSL_MUST_USE_RESULT StatusOr; 
 
// y_absl::StatusOr<T> 
// 
// The `y_absl::StatusOr<T>` class template is a union of an `y_absl::Status` object 
// and an object of type `T`. The `y_absl::StatusOr<T>` models an object that is 
// either a usable object, or an error (of type `y_absl::Status`) explaining why 
// such an object is not present. An `y_absl::StatusOr<T>` is typically the return 
// value of a function which may fail. 
// 
// An `y_absl::StatusOr<T>` can never hold an "OK" status (an 
// `y_absl::StatusCode::kOk` value); instead, the presence of an object of type 
// `T` indicates success. Instead of checking for a `kOk` value, use the 
// `y_absl::StatusOr<T>::ok()` member function. (It is for this reason, and code 
// readability, that using the `ok()` function is preferred for `y_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 `y_absl::StatusOr<T>` should be performed via 
// `operator*` or `operator->`, after a call to `ok()` confirms that the 
// `y_absl::StatusOr<T>` holds an object of type `T`: 
// 
// Example: 
// 
//   y_absl::StatusOr<int> i = GetCount(); 
//   if (i.ok()) { 
//     updated_total += *i 
//   } 
// 
// NOTE: using `y_absl::StatusOr<T>::value()` when no valid value is present will 
// throw an exception if exceptions are enabled or terminate the process when 
// exceptions are not enabled. 
// 
// Example: 
// 
//   StatusOr<Foo> result = DoBigCalculationThatCouldFail(); 
//   const Foo& foo = result.value();    // Crash/exception if no value present 
//   foo.DoSomethingCool(); 
// 
// A `y_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 
// `y_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 y_absl::Status(y_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 `y_absl::StatusOr` with an `y_absl::StatusCode::kUnknown` 
  // status. This constructor is marked 'explicit' to prevent usages in return 
  // values such as 'return {};', under the misconception that 
  // `y_absl::StatusOr<std::vector<int>>` will be initialized with an empty 
  // vector, instead of an `y_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 `y_absl::StatusOr<T>` from an `y_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, 
      y_absl::enable_if_t< 
          y_absl::conjunction< 
              y_absl::negation<std::is_same<T, U>>, 
              std::is_constructible<T, const U&>, 
              std::is_convertible<const U&, T>, 
              y_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, 
      y_absl::enable_if_t< 
          y_absl::conjunction< 
              y_absl::negation<std::is_same<T, U>>, 
              std::is_constructible<T, const U&>, 
              y_absl::negation<std::is_convertible<const U&, T>>, 
              y_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, 
      y_absl::enable_if_t< 
          y_absl::conjunction< 
              y_absl::negation<std::is_same<T, U>>, std::is_constructible<T, U&&>, 
              std::is_convertible<U&&, T>, 
              y_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, 
      y_absl::enable_if_t< 
          y_absl::conjunction< 
              y_absl::negation<std::is_same<T, U>>, std::is_constructible<T, U&&>, 
              y_absl::negation<std::is_convertible<U&&, T>>, 
              y_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 `y_absl::StatusOr<T>` through assignment from an 
  // `y_absl::StatusOr<U>` when: 
  // 
  //   * Both `y_absl::StatusOr<T>` and `y_absl::StatusOr<U>` are OK by assigning 
  //     `U` to `T` directly. 
  //   * `y_absl::StatusOr<T>` is OK and `y_absl::StatusOr<U>` contains an error 
  //      code by destroying `y_absl::StatusOr<T>`'s value and assigning from 
  //      `y_absl::StatusOr<U>' 
  //   * `y_absl::StatusOr<T>` contains an error code and `y_absl::StatusOr<U>` is 
  //      OK by directly initializing `T` from `U`. 
  //   * Both `y_absl::StatusOr<T>` and `y_absl::StatusOr<U>` contain an error 
  //     code by assigning the `Status` in `y_absl::StatusOr<U>` to 
  //     `y_absl::StatusOr<T>` 
  // 
  // These overloads only apply if `y_absl::StatusOr<T>` is constructible and 
  // assignable from `y_absl::StatusOr<U>` and `StatusOr<T>` cannot be directly 
  // assigned from `StatusOr<U>`. 
  template < 
      typename U, 
      y_absl::enable_if_t< 
          y_absl::conjunction< 
              y_absl::negation<std::is_same<T, U>>, 
              std::is_constructible<T, const U&>, 
              std::is_assignable<T, const U&>, 
              y_absl::negation< 
                  internal_statusor:: 
                      IsConstructibleOrConvertibleOrAssignableFromStatusOr< 
                          T, U>>>::value, 
          int> = 0> 
  StatusOr& operator=(const StatusOr<U>& other) { 
    this->Assign(other); 
    return *this; 
  } 
  template < 
      typename U, 
      y_absl::enable_if_t< 
          y_absl::conjunction< 
              y_absl::negation<std::is_same<T, U>>, std::is_constructible<T, U&&>, 
              std::is_assignable<T, U&&>, 
              y_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 `y_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 
  // `y_absl::Status`. This constructor is explicit if an only if `U` is not of 
  // type `y_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 y_absl::OkStatus() here will have the effect 
  // of passing y_absl::StatusCode::kInternal as a fallback. 
  template < 
      typename U = y_absl::Status, 
      y_absl::enable_if_t< 
          y_absl::conjunction< 
              std::is_convertible<U&&, y_absl::Status>, 
              std::is_constructible<y_absl::Status, U&&>, 
              y_absl::negation<std::is_same<y_absl::decay_t<U>, y_absl::StatusOr<T>>>, 
              y_absl::negation<std::is_same<y_absl::decay_t<U>, T>>, 
              y_absl::negation<std::is_same<y_absl::decay_t<U>, y_absl::in_place_t>>, 
              y_absl::negation<internal_statusor::HasConversionOperatorToStatusOr< 
                  T, U&&>>>::value, 
          int> = 0> 
  StatusOr(U&& v) : Base(std::forward<U>(v)) {} 
 
  template < 
      typename U = y_absl::Status, 
      y_absl::enable_if_t< 
          y_absl::conjunction< 
              y_absl::negation<std::is_convertible<U&&, y_absl::Status>>, 
              std::is_constructible<y_absl::Status, U&&>, 
              y_absl::negation<std::is_same<y_absl::decay_t<U>, y_absl::StatusOr<T>>>, 
              y_absl::negation<std::is_same<y_absl::decay_t<U>, T>>, 
              y_absl::negation<std::is_same<y_absl::decay_t<U>, y_absl::in_place_t>>, 
              y_absl::negation<internal_statusor::HasConversionOperatorToStatusOr< 
                  T, U&&>>>::value, 
          int> = 0> 
  explicit StatusOr(U&& v) : Base(std::forward<U>(v)) {} 
 
  template < 
      typename U = y_absl::Status, 
      y_absl::enable_if_t< 
          y_absl::conjunction< 
              std::is_convertible<U&&, y_absl::Status>, 
              std::is_constructible<y_absl::Status, U&&>, 
              y_absl::negation<std::is_same<y_absl::decay_t<U>, y_absl::StatusOr<T>>>, 
              y_absl::negation<std::is_same<y_absl::decay_t<U>, T>>, 
              y_absl::negation<std::is_same<y_absl::decay_t<U>, y_absl::in_place_t>>, 
              y_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<y_absl::conjunction< 
          std::is_constructible<T, U&&>, std::is_assignable<T&, U&&>, 
          y_absl::disjunction< 
              std::is_same<y_absl::remove_cv_t<y_absl::remove_reference_t<U>>, T>, 
              y_absl::conjunction< 
                  y_absl::negation<std::is_convertible<U&&, y_absl::Status>>, 
                  y_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(y_absl::in_place_t, Args&&... args); 
  template <typename U, typename... Args> 
  explicit StatusOr(y_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 constructor is disabled if `U` is a `StatusOr<J>`, where
  // `J` is convertible to `T`.
  template < 
      typename U = T, 
      y_absl::enable_if_t< 
          y_absl::conjunction< 
              internal_statusor::IsDirectInitializationValid<T, U&&>, 
              std::is_constructible<T, U&&>, std::is_convertible<U&&, T>, 
              y_absl::disjunction< 
                  std::is_same<y_absl::remove_cv_t<y_absl::remove_reference_t<U>>, 
                               T>, 
                  y_absl::conjunction< 
                      y_absl::negation<std::is_convertible<U&&, y_absl::Status>>, 
                      y_absl::negation< 
                          internal_statusor::HasConversionOperatorToStatusOr< 
                              T, U&&>>>>>::value, 
          int> = 0> 
  StatusOr(U&& u)  // NOLINT 
      : StatusOr(y_absl::in_place, std::forward<U>(u)) {}
 
  template < 
      typename U = T, 
      y_absl::enable_if_t< 
          y_absl::conjunction< 
              internal_statusor::IsDirectInitializationValid<T, U&&>, 
              y_absl::disjunction< 
                  std::is_same<y_absl::remove_cv_t<y_absl::remove_reference_t<U>>, 
                               T>, 
                  y_absl::conjunction< 
                      y_absl::negation<std::is_constructible<y_absl::Status, U&&>>, 
                      y_absl::negation< 
                          internal_statusor::HasConversionOperatorToStatusOr< 
                              T, U&&>>>>, 
              std::is_constructible<T, U&&>, 
              y_absl::negation<std::is_convertible<U&&, T>>>::value, 
          int> = 0> 
  explicit StatusOr(U&& u)  // NOLINT 
      : StatusOr(y_absl::in_place, std::forward<U>(u)) {}
 
  // StatusOr<T>::ok() 
  // 
  // Returns whether or not this `y_absl::StatusOr<T>` holds a `T` value. This 
  // member function is analagous to `y_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 `y_absl::Status` contained within the 
  // `y_absl::StatusOr<T>`. If `y_absl::StatusOr<T>` contains a `T`, then this 
  // function returns `y_absl::OkStatus()`. 
  const Status& status() const&;
  Status status() &&; 
 
  // StatusOr<T>::value() 
  // 
  // Returns a reference to the held value if `this->ok()`. Otherwise, throws 
  // `y_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& ABSL_ATTRIBUTE_LIFETIME_BOUND;
  T& value() & ABSL_ATTRIBUTE_LIFETIME_BOUND;
  const T&& value() const&& ABSL_ATTRIBUTE_LIFETIME_BOUND;
  T&& value() && ABSL_ATTRIBUTE_LIFETIME_BOUND;
 
  // 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 
  // `y_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& ABSL_ATTRIBUTE_LIFETIME_BOUND;
  T& operator*() & ABSL_ATTRIBUTE_LIFETIME_BOUND;
  const T&& operator*() const&& ABSL_ATTRIBUTE_LIFETIME_BOUND;
  T&& operator*() && ABSL_ATTRIBUTE_LIFETIME_BOUND;
 
  // 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 ABSL_ATTRIBUTE_LIFETIME_BOUND;
  T* operator->() ABSL_ATTRIBUTE_LIFETIME_BOUND;
 
  // StatusOr<T>::value_or() 
  // 
  // Returns the current value if `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_ = y_absl::OkStatus(); 
    } 
    return this->data_; 
  } 
 
  template < 
      typename U, typename... Args, 
      y_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_ = y_absl::OkStatus(); 
    } 
    return this->data_; 
  } 
 
 private: 
  using internal_statusor::StatusOrData<T>::Assign; 
  template <typename U> 
  void Assign(const y_absl::StatusOr<U>& other); 
  template <typename U> 
  void Assign(y_absl::StatusOr<U>&& other); 
}; 
 
// operator==() 
// 
// This operator checks the equality of two `y_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 `y_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(y_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(y_absl::in_place_t, Args&&... args) 
    : Base(y_absl::in_place, std::forward<Args>(args)...) {} 
 
template <typename T> 
template <typename U, typename... Args> 
StatusOr<T>::StatusOr(y_absl::in_place_t, std::initializer_list<U> ilist, 
                      Args&&... args) 
    : Base(y_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 y_absl 
 
#endif  // ABSL_STATUS_STATUSOR_H_