Programming Support¶

General information¶

const BuildInfo &arrow::GetBuildInfo()¶

Get runtime build info.

The returned values correspond to exact loaded version of the Arrow library, rather than the values frozen at application compile-time through the ARROW_* preprocessor definitions.

struct arrow::BuildInfo¶

Public Members

int version¶: The packed version number, e.g. 1002003 (decimal) for Arrow 1.2.3.

int version_major¶: The “major” version number, e.g. 1 for Arrow 1.2.3.

int version_minor¶: The “minor” version number, e.g. 2 for Arrow 1.2.3.

int version_patch¶: The “patch” version number, e.g. 3 for Arrow 1.2.3.

std::string version_string¶: The version string, e.g. “1.2.3”.

Error return and reporting¶

class arrow::Status : public arrow::util::EqualityComparable<Status>, public arrow::util::ToStringOstreamable<Status>¶

Status outcome object (success or error)

The Status object is an object holding the outcome of an operation. The outcome is represented as a StatusCode, either success (StatusCode::OK) or an error (any other of the StatusCode enumeration values).

Additionally, if an error occurred, a specific error message is generally attached.

Public Functions

Status(StatusCode code, std::string msg, std::shared_ptr<StatusDetail> detail)¶: Pluggable constructor for use by sub-systems. detail cannot be null.

bool ok() const¶: Return true iff the status indicates success.

bool IsOutOfMemory() const¶: Return true iff the status indicates an out-of-memory error.

bool IsKeyError() const¶: Return true iff the status indicates a key lookup error.

bool IsInvalid() const¶: Return true iff the status indicates invalid data.

bool IsIOError() const¶: Return true iff the status indicates an IO-related failure.

bool IsCapacityError() const¶: Return true iff the status indicates a container reaching capacity limits.

bool IsIndexError() const¶: Return true iff the status indicates an out of bounds index.

bool IsTypeError() const¶: Return true iff the status indicates a type error.

bool IsUnknownError() const¶: Return true iff the status indicates an unknown error.

bool IsNotImplemented() const¶: Return true iff the status indicates an unimplemented operation.

bool IsSerializationError() const¶: Return true iff the status indicates a (de)serialization failure.

bool IsRError() const¶: Return true iff the status indicates a R-originated error.

std::string ToString() const¶

Return a string representation of this status suitable for printing.

The string “OK” is returned for success.

std::string CodeAsString() const¶: Return a string representation of the status code, without the message text or POSIX code information.

StatusCode code() const¶: Return the StatusCode value attached to this status.

std::string message() const¶: Return the specific error message attached to this status.

Status WithDetail(std::shared_ptr<StatusDetail> new_detail) const¶: Return a new Status copying the existing status, but updating with the existing detail.

template<typename ...Args> Status WithMessage(Args&&... args) const¶: Return a new Status with changed message, copying the existing status code and detail.

Public Static Functions

Status OK()¶: Return a success status.

template<typename ...Args> Status OutOfMemory(Args&&... args)¶: Return an error status for out-of-memory conditions.

template<typename ...Args> Status KeyError(Args&&... args)¶: Return an error status for failed key lookups (e.g. column name in a table)

template<typename ...Args> Status TypeError(Args&&... args)¶: Return an error status for type errors (such as mismatching data types)

template<typename ...Args> Status UnknownError(Args&&... args)¶: Return an error status for unknown errors.

template<typename ...Args> Status NotImplemented(Args&&... args)¶: Return an error status when an operation or a combination of operation and data types is unimplemented.

template<typename ...Args> Status Invalid(Args&&... args)¶: Return an error status for invalid data (for example a string that fails parsing)

template<typename ...Args> Status IndexError(Args&&... args)¶: Return an error status when an index is out of bounds.

template<typename ...Args> Status CapacityError(Args&&... args)¶: Return an error status when a container’s capacity would exceed its limits.

template<typename ...Args> Status IOError(Args&&... args)¶: Return an error status when some IO-related operation failed.

template<typename ...Args> Status SerializationError(Args&&... args)¶: Return an error status when some (de)serialization operation failed.

class arrow::StatusDetail¶

An opaque class that allows subsystems to retain additional information inside the Status.

Subclassed by arrow::flight::FlightStatusDetail, arrow::flight::FlightWriteSizeStatusDetail

Public Functions

const char *type_id() const = 0¶: Return a unique id for the type of the StatusDetail (effectively a poor man’s substitute for RTTI).

std::string ToString() const = 0¶: Produce a human-readable description of this status.

template<class T> class arrow::Result : public arrow::util::EqualityComparable<Result<T>>¶

A class for representing either a usable value, or an error.

A Result object either contains a value of type T or a Status object explaining why such a value is not present. The type T must be copy-constructible and/or move-constructible.

The state of a Result object may be determined by calling ok() or status(). The ok() method returns true if the object contains a valid value. The status() method returns the internal Status object. A Result object that contains a valid value will return an OK Status for a call to status().

A value of type T may be extracted from a Result object through a call to ValueOrDie(). This function should only be called if a call to ok() returns true. Sample usage:

 arrow::Result<Foo> result = CalculateFoo();
 if (result.ok()) {
   Foo foo = result.ValueOrDie();
   foo.DoSomethingCool();
 } else {
   ARROW_LOG(ERROR) << result.status();
}

If T is a move-only type, like std::unique_ptr<>, then the value should only be extracted after invoking std::move() on the Result object. Sample usage:

arrow::Result<std::unique_ptr<Foo>> result = CalculateFoo();
if (result.ok()) {
  std::unique_ptr<Foo> foo = std::move(result).ValueOrDie();
  foo->DoSomethingCool();
} else {
  ARROW_LOG(ERROR) << result.status();
}

Result is provided for the convenience of implementing functions that return some value but may fail during execution. For instance, consider a function with the following signature:

arrow::Status CalculateFoo(int *output);

This function may instead be written as:

arrow::Result<int> CalculateFoo();

Public Functions

Result()¶

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.

Result(const Status &status)¶

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.

Parameters

status: The non-OK Status object to initialize to.

template<typename U, typename E = typename std::enable_if<std::is_constructible<T, U>::value && std::is_convertible<U, T>::value && !std::is_same<typename std::remove_reference<typename std::remove_cv::type>::type, Status>::value>::type> Result(U &&value) noexcept¶

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.

Parameters

value: The value to initialize to.

Result(T &&value) noexcept¶

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 T, implicitly converting it to a Result<T> object.

Parameters

value: The value to initialize to.

Result(const Result &other)¶

Copy constructor.

This constructor needs to be explicitly defined because the presence of the move-assignment operator deletes the default copy constructor. In such a scenario, since the deleted copy constructor has stricter binding rules than the templated copy constructor, the templated constructor cannot act as a copy constructor, and any attempt to copy-construct a Result object results in a compilation error.

Parameters

other: The value to copy from.

template<typename U, typename E = typename std::enable_if<std::is_constructible<T, const U&>::value && std::is_convertible<U, T>::value>::type> Result(const Result &other)¶

Templatized constructor that constructs a Result<T> from a const reference to a Result.

T must be implicitly constructible from const U &.

Parameters

other: The value to copy from.

Result &operator=(const Result &other)¶

Copy-assignment operator.

Parameters

other: The Result object to copy.

template<typename U, typename E = typename std::enable_if<std::is_constructible<T, U&&>::value && std::is_convertible<U, T>::value>::type> Result(Result &&other) noexcept¶

Templatized constructor which constructs a Result<T> by moving the contents of a Result.

T must be implicitly constructible from U &&.

Sets other to contain a non-OK status with aStatusError::Invalid error code.

Parameters

other: The Result object to move from and set to a non-OK status.

Result &operator=(Result &&other) noexcept¶

Move-assignment operator.

Sets other to an invalid state..

Parameters

other: The Result object to assign from and set to a non-OK status.

bool Equals(const Result &other) const¶: Compare to another Result.

bool ok() const¶

Indicates whether the object contains a T value.

Generally instead of accessing this directly you will want to use ASSIGN_OR_RAISE defined below.

Return: True if this Result object’s status is OK (i.e. a call to ok() returns true). If this function returns true, then it is safe to access the wrapped element through a call to ValueOrDie().

const Status &status() const¶

Equivalent to ok().

Gets the stored status object, or an OK status if a T value is stored.

Return: The stored non-OK status object, or an OK status if this object has a value.

const T &ValueOrDie() const &¶

Gets the stored T value.

This method should only be called if this Result object’s status is OK (i.e. a call to ok() returns true), otherwise this call will abort.

Return: The stored T value.

T &ValueOrDie() &¶

Gets a mutable reference to the stored T value.

This method should only be called if this Result object’s status is OK (i.e. a call to ok() returns true), otherwise this call will abort.

Return: The stored T value.

T ValueOrDie() &&¶

Moves and returns the internally-stored T value.

This method should only be called if this Result object’s status is OK (i.e. a call to ok() returns true), otherwise this call will abort. The Result object is invalidated after this call and will be updated to contain a non-OK status.

Return: The stored T value.

template<typename U, typename E = typename std::enable_if<std::is_constructible<U, T>::value>::type> Status Value(U *out) &&¶

Helper method for implementing Status returning functions in terms of semantically equivalent Result returning functions.

For example:

Status GetInt(int *out) { return GetInt().Value(out); }

T ValueOr(T alternative) &&¶: Move and return the internally stored value or alternative if an error is stored.

template<typename G> T ValueOrElse(G &&generate_alternative) &&¶: Retrieve the value if ok(), falling back to an alternative generated by the provided factory.

template<typename M> EnsureResult<typename std::result_of<M&&(T)>::type>::type Map(M &&m) &&¶: Apply a function to the internally stored value to produce a new result or propagate the stored error.

template<typename M> EnsureResult<typename std::result_of<M&&(const T&)>::type>::type Map(M &&m) const &¶: Apply a function to the internally stored value to produce a new result or propagate the stored error.

template<typename U, typename E = typename std::enable_if<std::is_constructible<U, T>::value>::type> Result As() &&¶: Cast the internally stored value to produce a new result or propagate the stored error.

template<typename U, typename E = typename std::enable_if<std::is_constructible<U, const T&>::value>::type> Result As() const &¶: Cast the internally stored value to produce a new result or propagate the stored error.

class ParquetException : public exception¶: Subclassed by parquet::HiddenColumnException, parquet::KeyAccessDeniedException, parquet::ParquetStatusException

ARROW_RETURN_NOT_OK(status)¶: Propagate any non-successful Status to the caller.

ARROW_ASSIGN_OR_RAISE(lhs, rexpr)¶

Execute an expression that returns a Result, extracting its value into the variable defined by lhs (or returning a Status on error).

Example: Assigning to a new value: ARROW_ASSIGN_OR_RAISE(auto value, MaybeGetValue(arg));

Example: Assigning to an existing value: ValueType value; ARROW_ASSIGN_OR_RAISE(value, MaybeGetValue(arg));

WARNING: ARROW_ASSIGN_OR_RAISE expands into multiple statements; it cannot be used in a single statement (e.g. as the body of an if statement without {})!

WARNING: ARROW_ASSIGN_OR_RAISE std::moves its right operand. If you have an lvalue Result which you don’t want to move out of cast appropriately.

PARQUET_THROW_NOT_OK(s)¶

PARQUET_ASSIGN_OR_THROW(lhs, rexpr)¶