Class Result

cpp/src/arrow/result.h:99–466

/// ```
template <class T>
class [[nodiscard]] Result : public util::EqualityComparable<Result<T>> {
  template <typename U>
  friend class Result;

  static_assert(!std::is_same<T, Status>::value,
                "this assert indicates you have probably made a metaprogramming error");

 public:
  using ValueType = T;

  /// Constructs a Result object that contains a non-OK status.
  ///
  /// This constructor is marked `explicit` to prevent attempts to `return {}`
  /// from a function with a return type of, for example,
  /// `Result<std::vector<int>>`. While `return {}` seems like it would return
  /// an empty vector, it will actually invoke the default constructor of
  /// Result.
  explicit Result() noexcept  // NOLINT(runtime/explicit)
      : status_(internal::UninitializedResult()) {}

  ~Result() noexcept { Destroy(); }

  /// Constructs a Result object with the given non-OK Status object. All
  /// calls to ValueOrDie() on this object will abort. The given `status` must
  /// not be an OK status, otherwise this constructor will abort.
  ///
  /// This constructor is not declared explicit so that a function with a return
  /// type of `Result<T>` can return a Status object, and the status will be
  /// implicitly converted to the appropriate return type as a matter of
  /// convenience.
  ///
  /// \param status The non-OK Status object to initialize to.
  Result(const Status& status) noexcept  // NOLINT(runtime/explicit)
      : status_(status) {
    if (ARROW_PREDICT_FALSE(status.ok())) {
      internal::DieWithMessage(std::string("Constructed with a non-error status: ") +
                               status.ToString());
    }
  }

  /// Constructs a Result object that contains `value`. The resulting object
  /// is considered to have an OK status. The wrapped element can be accessed
  /// with ValueOrDie().
  ///
  /// This constructor is made implicit so that a function with a return type of
  /// `Result<T>` can return an object of type `U &&`, implicitly converting
  /// it to a `Result<T>` object.
  ///
  /// Note that `T` must be implicitly constructible from `U`, and `U` must not
  /// be a (cv-qualified) Status or Status-reference type. Due to C++
  /// reference-collapsing rules and perfect-forwarding semantics, this
  /// constructor matches invocations that pass `value` either as a const
  /// reference or as an rvalue reference. Since Result needs to work for both
  /// reference and rvalue-reference types, the constructor uses perfect
  /// forwarding to avoid invalidating arguments that were passed by reference.
  /// See http://thbecker.net/articles/rvalue_references/section_08.html for
  /// additional details.
  ///