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//===----------------------------------------------------------------------===//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2021 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
//
//===----------------------------------------------------------------------===//
import Swift
@available(SwiftStdlib 5.1, *)
extension AsyncSequence {
/// Creates an asynchronous sequence that maps an error-throwing closure over
/// the base sequence’s elements, omitting results that don't return a value.
///
/// Use the `compactMap(_:)` method to transform every element received from
/// a base asynchronous sequence, while also discarding any `nil` results
/// from the closure. Typically, you use this to transform from one type of
/// element to another.
///
/// In this example, an asynchronous sequence called `Counter` produces `Int`
/// values from `1` to `5`. The closure provided to the `compactMap(_:)`
/// method takes each `Int` and looks up a corresponding `String` from a
/// `romanNumeralDict` dictionary. Since there is no key for `4`, the closure
/// returns `nil` in this case, which `compactMap(_:)` omits from the
/// transformed asynchronous sequence. When the value is `5`, the closure
/// throws `MyError`, terminating the sequence.
///
/// let romanNumeralDict: [Int: String] =
/// [1: "I", 2: "II", 3: "III", 5: "V"]
///
/// do {
/// let stream = Counter(howHigh: 5)
/// .compactMap { (value) throws -> String? in
/// if value == 5 {
/// throw MyError()
/// }
/// return romanNumeralDict[value]
/// }
/// for try await numeral in stream {
/// print(numeral, terminator: " ")
/// }
/// } catch {
/// print("Error: \(error)")
/// }
/// // Prints "I II III Error: MyError() "
///
/// - Parameter transform: An error-throwing mapping closure. `transform`
/// accepts an element of this sequence as its parameter and returns a
/// transformed value of the same or of a different type. If `transform`
/// throws an error, the sequence ends.
/// - Returns: An asynchronous sequence that contains, in order, the
/// non-`nil` elements produced by the `transform` closure. The sequence
/// ends either when the base sequence ends or when `transform` throws an
/// error.
@preconcurrency
@inlinable
public __consuming func compactMap<ElementOfResult>(
_ transform: @Sendable @escaping (Element) async throws -> ElementOfResult?
) -> AsyncThrowingCompactMapSequence<Self, ElementOfResult> {
return AsyncThrowingCompactMapSequence(self, transform: transform)
}
}
/// An asynchronous sequence that maps an error-throwing closure over the base
/// sequence’s elements, omitting results that don't return a value.
@available(SwiftStdlib 5.1, *)
public struct AsyncThrowingCompactMapSequence<Base: AsyncSequence, ElementOfResult> {
@usableFromInline
let base: Base
@usableFromInline
let transform: (Base.Element) async throws -> ElementOfResult?
@usableFromInline
init(
_ base: Base,
transform: @escaping (Base.Element) async throws -> ElementOfResult?
) {
self.base = base
self.transform = transform
}
}
@available(SwiftStdlib 5.1, *)
extension AsyncThrowingCompactMapSequence: AsyncSequence {
/// The type of element produced by this asynchronous sequence.
///
/// The compact map sequence produces whatever type of element its
/// transforming closure produces.
public typealias Element = ElementOfResult
/// The type of element produced by this asynchronous sequence.
///
/// The compact map sequence produces errors from either the base
/// sequence or the transforming closure.
public typealias Failure = any Error
/// The type of iterator that produces elements of the sequence.
public typealias AsyncIterator = Iterator
/// The iterator that produces elements of the compact map sequence.
public struct Iterator: AsyncIteratorProtocol {
public typealias Element = ElementOfResult
@usableFromInline
var baseIterator: Base.AsyncIterator
@usableFromInline
let transform: (Base.Element) async throws -> ElementOfResult?
@usableFromInline
var finished = false
@usableFromInline
init(
_ baseIterator: Base.AsyncIterator,
transform: @escaping (Base.Element) async throws -> ElementOfResult?
) {
self.baseIterator = baseIterator
self.transform = transform
}
/// Produces the next element in the compact map sequence.
///
/// This iterator calls `next()` on its base iterator; if this call returns
/// `nil`, `next()` returns `nil`. Otherwise, `next()` calls the
/// transforming closure on the received element, returning it if the
/// transform returns a non-`nil` value. If the transform returns `nil`,
/// this method continues to wait for further elements until it gets one
/// that transforms to a non-`nil` value. If calling the closure throws an
/// error, the sequence ends and `next()` rethrows the error.
@inlinable
public mutating func next() async throws -> ElementOfResult? {
while !finished {
guard let element = try await baseIterator.next() else {
finished = true
return nil
}
do {
if let transformed = try await transform(element) {
return transformed
}
} catch {
finished = true
throw error
}
}
return nil
}
/// Produces the next element in the compact map sequence.
///
/// This iterator calls `next()` on its base iterator; if this call
/// returns `nil`, `next()` returns `nil`. Otherwise, `next()`
/// calls the transforming closure on the received element, returning it if
/// the transform returns a non-`nil` value. If the transform returns `nil`,
/// this method continues to wait for further elements until it gets one
/// that transforms to a non-`nil` value. If calling the closure throws an
/// error, the sequence ends and `next()` rethrows the error.
@available(SwiftStdlib 6.0, *)
@inlinable
public mutating func next(isolation actor: isolated (any Actor)?) async throws(Failure) -> ElementOfResult? {
while !finished {
guard let element = try await baseIterator.next(isolation: actor) else {
finished = true
return nil
}
do {
if let transformed = try await transform(element) {
return transformed
}
} catch {
finished = true
throw error
}
}
return nil
}
}
@inlinable
public __consuming func makeAsyncIterator() -> Iterator {
return Iterator(base.makeAsyncIterator(), transform: transform)
}
}
@available(SwiftStdlib 5.1, *)
extension AsyncThrowingCompactMapSequence: @unchecked Sendable
where Base: Sendable,
Base.Element: Sendable { }
@available(SwiftStdlib 5.1, *)
extension AsyncThrowingCompactMapSequence.Iterator: @unchecked Sendable
where Base.AsyncIterator: Sendable,
Base.Element: Sendable { }
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