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Result.swift
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Result.swift
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//===----------------------------------------------------------------------===//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2018 - 2024 Apple Inc. and the Swift project authors
// Licensed under Apache License v2.0 with Runtime Library Exception
//
// See https://swift.org/LICENSE.txt for license information
// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
//
//===----------------------------------------------------------------------===//
/// A value that represents either a success or a failure, including an
/// associated value in each case.
@frozen
public enum Result<Success: ~Copyable, Failure: Error> {
/// A success, storing a `Success` value.
case success(Success)
/// A failure, storing a `Failure` value.
case failure(Failure)
}
extension Result: Copyable where Success: Copyable {}
extension Result: Sendable where Success: Sendable & ~Copyable {}
extension Result: Equatable where Success: Equatable, Failure: Equatable {}
extension Result: Hashable where Success: Hashable, Failure: Hashable {}
extension Result {
/// Returns a new result, mapping any success value using the given
/// transformation.
///
/// Use this method when you need to transform the value of a `Result`
/// instance when it represents a success. The following example transforms
/// the integer success value of a result into a string:
///
/// func getNextInteger() -> Result<Int, Error> { /* ... */ }
///
/// let integerResult = getNextInteger()
/// // integerResult == .success(5)
/// let stringResult = integerResult.map { String($0) }
/// // stringResult == .success("5")
///
/// - Parameter transform: A closure that takes the success value of this
/// instance.
/// - Returns: A `Result` instance with the result of evaluating `transform`
/// as the new success value if this instance represents a success.
@_alwaysEmitIntoClient
@_disfavoredOverload // FIXME: Workaround for source compat issue with
// functions that used to shadow the original map
// (rdar://125016028)
public func map<NewSuccess: ~Copyable>(
_ transform: (Success) -> NewSuccess
) -> Result<NewSuccess, Failure> {
switch self {
case let .success(success):
return .success(transform(success))
case let .failure(failure):
return .failure(failure)
}
}
@_spi(SwiftStdlibLegacyABI) @available(swift, obsoleted: 1)
@_silgen_name("$ss6ResultO3mapyAByqd__q_Gqd__xXElF")
@usableFromInline
internal func __abi_map<NewSuccess>(
_ transform: (Success) -> NewSuccess
) -> Result<NewSuccess, Failure> {
switch self {
case let .success(success):
return .success(transform(success))
case let .failure(failure):
return .failure(failure)
}
}
}
@_disallowFeatureSuppression(NoncopyableGenerics)
extension Result where Success: ~Copyable {
// FIXME(NCG): Make this public.
@_alwaysEmitIntoClient
public consuming func _consumingMap<NewSuccess: ~Copyable>(
_ transform: (consuming Success) -> NewSuccess
) -> Result<NewSuccess, Failure> {
switch consume self {
case let .success(success):
return .success(transform(consume success))
case let .failure(failure):
return .failure(consume failure)
}
}
// FIXME(NCG): Make this public.
@_alwaysEmitIntoClient
public borrowing func _borrowingMap<NewSuccess: ~Copyable>(
_ transform: (borrowing Success) -> NewSuccess
) -> Result<NewSuccess, Failure> {
switch self {
case .success(let success):
return .success(transform(success))
case let .failure(failure):
return .failure(failure)
}
}
}
extension Result where Success: ~Copyable {
/// Returns a new result, mapping any failure value using the given
/// transformation.
///
/// Use this method when you need to transform the value of a `Result`
/// instance when it represents a failure. The following example transforms
/// the error value of a result by wrapping it in a custom `Error` type:
///
/// struct DatedError: Error {
/// var error: Error
/// var date: Date
///
/// init(_ error: Error) {
/// self.error = error
/// self.date = Date()
/// }
/// }
///
/// let result: Result<Int, Error> = // ...
/// // result == .failure(<error value>)
/// let resultWithDatedError = result.mapError { DatedError($0) }
/// // result == .failure(DatedError(error: <error value>, date: <date>))
///
/// - Parameter transform: A closure that takes the failure value of the
/// instance.
/// - Returns: A `Result` instance with the result of evaluating `transform`
/// as the new failure value if this instance represents a failure.
@_alwaysEmitIntoClient
public consuming func mapError<NewFailure>(
_ transform: (Failure) -> NewFailure
) -> Result<Success, NewFailure> {
switch consume self {
case let .success(success):
return .success(consume success)
case let .failure(failure):
return .failure(transform(failure))
}
}
}
@_disallowFeatureSuppression(NoncopyableGenerics)
extension Result {
@_spi(SwiftStdlibLegacyABI) @available(swift, obsoleted: 1)
@usableFromInline
internal func mapError<NewFailure>(
_ transform: (Failure) -> NewFailure
) -> Result<Success, NewFailure> {
switch self {
case let .success(success):
return .success(success)
case let .failure(failure):
return .failure(transform(failure))
}
}
}
extension Result {
/// Returns a new result, mapping any success value using the given
/// transformation and unwrapping the produced result.
///
/// Use this method to avoid a nested result when your transformation
/// produces another `Result` type.
///
/// In this example, note the difference in the result of using `map` and
/// `flatMap` with a transformation that returns a result type.
///
/// func getNextInteger() -> Result<Int, Error> {
/// .success(4)
/// }
/// func getNextAfterInteger(_ n: Int) -> Result<Int, Error> {
/// .success(n + 1)
/// }
///
/// let result = getNextInteger().map { getNextAfterInteger($0) }
/// // result == .success(.success(5))
///
/// let result = getNextInteger().flatMap { getNextAfterInteger($0) }
/// // result == .success(5)
///
/// - Parameter transform: A closure that takes the success value of the
/// instance.
/// - Returns: A `Result` instance, either from the closure or the previous
/// `.failure`.
@_alwaysEmitIntoClient
@_disfavoredOverload // FIXME: Workaround for source compat issue with
// functions that used to shadow the original flatMap
// (rdar://125016028)
public func flatMap<NewSuccess: ~Copyable>(
_ transform: (Success) -> Result<NewSuccess, Failure>
) -> Result<NewSuccess, Failure> {
switch self {
case let .success(success):
return transform(success)
case let .failure(failure):
return .failure(failure)
}
}
@_spi(SwiftStdlibLegacyABI) @available(swift, obsoleted: 1)
@_silgen_name("$ss6ResultO7flatMapyAByqd__q_GADxXElF")
@usableFromInline
internal func __abi_flatMap<NewSuccess>(
_ transform: (Success) -> Result<NewSuccess, Failure>
) -> Result<NewSuccess, Failure> {
switch self {
case let .success(success):
return transform(success)
case let .failure(failure):
return .failure(failure)
}
}
}
@_disallowFeatureSuppression(NoncopyableGenerics)
extension Result where Success: ~Copyable {
// FIXME(NCG): Make this public.
@_alwaysEmitIntoClient
public consuming func _consumingFlatMap<NewSuccess: ~Copyable>(
_ transform: (consuming Success) -> Result<NewSuccess, Failure>
) -> Result<NewSuccess, Failure> {
switch consume self {
case let .success(success):
return transform(consume success)
case let .failure(failure):
return .failure(failure)
}
}
// FIXME(NCG): Make this public.
@_alwaysEmitIntoClient
public borrowing func _borrowingFlatMap<NewSuccess: ~Copyable>(
_ transform: (borrowing Success) -> Result<NewSuccess, Failure>
) -> Result<NewSuccess, Failure> {
switch self {
case .success(let success):
return transform(success)
case let .failure(failure):
return .failure(failure)
}
}
}
extension Result where Success: ~Copyable {
/// Returns a new result, mapping any failure value using the given
/// transformation and unwrapping the produced result.
///
/// - Parameter transform: A closure that takes the failure value of the
/// instance.
/// - Returns: A `Result` instance, either from the closure or the previous
/// `.success`.
@_alwaysEmitIntoClient
public consuming func flatMapError<NewFailure>(
_ transform: (Failure) -> Result<Success, NewFailure>
) -> Result<Success, NewFailure> {
switch consume self {
case let .success(success):
return .success(success)
case let .failure(failure):
return transform(failure)
}
}
}
extension Result {
@_spi(SwiftStdlibLegacyABI) @available(swift, obsoleted: 1)
@_silgen_name("$ss6ResultO12flatMapErroryAByxqd__GADq_XEs0D0Rd__lF")
@usableFromInline
internal func __abi_flatMapError<NewFailure>(
_ transform: (Failure) -> Result<Success, NewFailure>
) -> Result<Success, NewFailure> {
switch self {
case let .success(success):
return .success(success)
case let .failure(failure):
return transform(failure)
}
}
}
extension Result where Success: ~Copyable {
/// Returns the success value as a throwing expression.
///
/// Use this method to retrieve the value of this result if it represents a
/// success, or to catch the value if it represents a failure.
///
/// let integerResult: Result<Int, Error> = .success(5)
/// do {
/// let value = try integerResult.get()
/// print("The value is \(value).")
/// } catch {
/// print("Error retrieving the value: \(error)")
/// }
/// // Prints "The value is 5."
///
/// - Returns: The success value, if the instance represents a success.
/// - Throws: The failure value, if the instance represents a failure.
@_alwaysEmitIntoClient
public consuming func get() throws(Failure) -> Success {
switch consume self {
case let .success(success):
return success
case let .failure(failure):
throw failure
}
}
}
extension Result where Success: ~Copyable {
/// Creates a new result by evaluating a throwing closure, capturing the
/// returned value as a success, or any thrown error as a failure.
///
/// - Parameter body: A potentially throwing closure to evaluate.
@_alwaysEmitIntoClient
public init(catching body: () throws(Failure) -> Success) {
do {
self = .success(try body())
} catch {
self = .failure(error)
}
}
}
extension Result {
/// ABI: Historical get() throws
@_spi(SwiftStdlibLegacyABI) @available(swift, obsoleted: 1)
@_silgen_name("$ss6ResultO3getxyKF")
@usableFromInline
func __abi_get() throws -> Success {
switch self {
case let .success(success):
return success
case let .failure(failure):
throw failure
}
}
}
extension Result where Failure == Swift.Error {
/// ABI: Historical init(catching:)
@_spi(SwiftStdlibLegacyABI) @available(swift, obsoleted: 1)
@_silgen_name("$ss6ResultOss5Error_pRs_rlE8catchingAByxsAC_pGxyKXE_tcfC")
@usableFromInline
init(__abi_catching body: () throws(Failure) -> Success) {
do {
self = .success(try body())
} catch {
self = .failure(error)
}
}
}