folly::Expected

Synopsis

Declared in <folly/Expected.h>

template<
    class V,
    class E>
class Expected final

Type Aliases

Name	Description
`error_type`	The type of the contained error.
`promise_type`	The coroutine promise type used when an Expected is a coroutine result.
`rebind`	Rebinds this Expected to a new value type while keeping the error type.
`value_type`	The type of the contained value.

Member Functions

Name	Description
`Expected` [constructor]	Constructors
`operator=`	Assignment operators
`emplace`	Constructs a new value in place, replacing any current contents.
`error`	Accesses the stored error, throwing if none is present.
`get_pointer`	`get_pointer` overloads
`hasError`	Reports whether the Expected holds an error.
`hasValue`	Reports whether the Expected holds a value.
`onError`	`onError` overloads
`operator*`	Dereferences to the stored value without checking.
`operator->`	Accesses members of the stored value.
`orElse`	`orElse` overloads
`swap`	swap
`then`	`then` overloads
`thenOrThrow`	`thenOrThrow` overloads
`value`	Accesses the stored value, throwing if none is present.
`value_or`	Returns the stored value, or a default when in the error state.
`operator bool`	Tests whether the Expected holds a value.

Using Declarations

Name
`uninitializedByException`

Friends

Name	Description
`folly::expected_detail::PromiseReturn`	Coroutine return object that materializes an Expected from a promise.
`folly::operator<`	Orders two Expected values, treating errors as less than values.
`folly::operator==`	Relational Operators
`folly::expected_detail::expected_detail_ExpectedHelper::ExpectedHelper`	Static helpers implementing the Expected continuation operations.
`folly::expected_detail::ExpectedStorage`	Storage backing an Expected, holding either a value or an error.
`folly::Expected`	Forward declarations

Non-Member Functions

Name	Description
`get_pointer`	Returns a pointer to the value of an Expected, or null on error.
`get_pointer`	Returns a pointer to the value of an Expected, or null on error.
`makeExpected`	For constructing an Expected object from a value, with the specified Error type. Usage is as follows:
`operator co_await`	Enables `co_await` on an Expected to unwrap its value or propagate its error.
`operator!=`	Deleted: comparing an Expected with a bare value is not allowed.
`operator!=`	Compares two Expected values for inequality.
`operator<`	Deleted: comparing an Expected with a bare value is not allowed.
`operator<`	Orders two Expected values, treating errors as less than values.
`operator<=`	Deleted: comparing an Expected with a bare value is not allowed.
`operator<=`	Orders two Expected values.
`operator==`	Deleted: comparing an Expected with a bare value is not allowed.
`operator==`	Compares two Expected values for equality.
`operator>`	Orders two Expected values.
`operator>`	Deleted: comparing an Expected with a bare value is not allowed.
`operator>=`	Orders two Expected values.
`operator>=`	Deleted: comparing an Expected with a bare value is not allowed.
`parseTo`	Parse a StringPiece into a std::string_view, consuming all input.
`parseTo`	Parse a StringPiece into a std::string, consuming all input.
`parseTo`	Parsing strings to numeric types.
`parseTo`	Parse a StringPiece into any folly string type, consuming all input.
`parseTo`	Parse a StringPiece into a StringPiece (identity, consuming all input).
`parseTo`	Parse a StringPiece into an fbstring, consuming all input.
`parseTo`	Custom Conversions
`swap`	swap Expected values
`tryDecodeVarint`	A variant of decodeVarint() that does not throw on error. Useful in contexts where only part of a serialized varint may be attempted to be decoded, e.g., when a serialized varint arrives on the boundary of a network packet.
`trySplitTo`	Try to split a string into a fixed number of fields by delimiter, using folly::tryTo<> for conversions. types by delimiter. - On success, all output values will be initialized and the 'Unit{}' value is returned. Arguments are assigned in reverse order. - On failure, the first failing 'ConversionCode' is returned with its associated substring in a 'SubstringConversionCode'. - String splitting is performed prior to each conversion; field values will not contain the delimiter. - All custom error codes are mapped to ConversionCode::CUSTOM.
`tryTo`	tryTo/to that take the strings by pointer so the caller gets information about how much of the string was consumed by the conversion. These do not check for trailing whitespace.
`tryTo`	String or StringPiece to target conversion. Accepts leading and trailing whitespace, but no non-space trailing characters.
`tryTo`	Checked conversion from any type to an enum, returning an Expected.
`tryTo`	std::chrono::duration to struct timeval
`tryTo`	struct timespec to std::chrono::duration
`tryTo`	struct timeval to std::chrono::duration
`tryTo`	Checked conversion between arithmetic types, returning an Expected.
`tryTo`	Enum to anything and back
`tryTo`	timespec or timeval to std::chrono::time_point
`tryTo`	Unchecked conversion from arithmetic to boolean. This is different from the other arithmetic conversions because we use the C convention of treating any non-zero value as true, instead of range checking.
`tryTo`	overloadbrief to, but return an Expected
`tryTo`	std::chrono::time_point to timespec or timeval
`tryTo`	std::chrono::duration to struct timespec
`tryTo`	String represented as a pair of pointers to char to unsigned integrals. Assumes NO whitespace before or after.
`settings::convertTo`	Like parseTo in folly/Conv.h, but the "source" is SettingValueAndMetadata instead of a StringPiece. Defaults to folly::tryTo<T>(StringPiece) but can be overridden using ADL for user defined types.
`settings::tryTo`	Conversion functions for converting a SettingValueAndMetadata to a setting type T. Implementation is similar to folly/Conv and allows for customization using the convertTo function above.