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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 the given error-throwing
/// closure over the asynchronous sequence’s elements.
///
/// Use the `map(_:)` method to transform every element received from a base
/// asynchronous sequence. 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 `map(_:)` method
/// takes each `Int` and looks up a corresponding `String` from a
/// `romanNumeralDict` dictionary. This means the outer `for await in` loop
/// iterates over `String` instances instead of the underlying `Int` values
/// that `Counter` produces. Also, the dictionary doesn't provide a key for
/// `4`, and the closure throws an error for any key it can't look up, so
/// receiving this value from `Counter` ends the modified sequence with an
/// error.
///
/// let romanNumeralDict: [Int: String] =
/// [1: "I", 2: "II", 3: "III", 5: "V"]
///
/// do {
/// let stream = Counter(howHigh: 5)
/// .map { (value) throws -> String in
/// guard let roman = romanNumeralDict[value] else {
/// throw MyError()
/// }
/// return roman
/// }
/// for try await numeral in stream {
/// print(numeral, terminator: " ")
/// }
/// } catch {
/// print("Error: \(error)")
/// }
/// // Prints "I II III Error: MyError() "
///
/// - Parameter transform: A 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. `transform` can also throw an error, which
/// ends the transformed sequence.
/// - Returns: An asynchronous sequence that contains, in order, the elements
/// produced by the `transform` closure.
@preconcurrency
@inlinable
public __consuming func map<Transformed>(
_ transform: @Sendable @escaping (Element) async throws -> Transformed
) -> AsyncThrowingMapSequence<Self, Transformed> {
return AsyncThrowingMapSequence(self, transform: transform)
}
}
/// An asynchronous sequence that maps the given error-throwing closure over the
/// asynchronous sequence’s elements.
@available(SwiftStdlib 5.1, *)
public struct AsyncThrowingMapSequence<Base: AsyncSequence, Transformed> {
@usableFromInline
let base: Base
@usableFromInline
let transform: (Base.Element) async throws -> Transformed
@usableFromInline
init(
_ base: Base,
transform: @escaping (Base.Element) async throws -> Transformed
) {
self.base = base
self.transform = transform
}
}
@available(SwiftStdlib 5.1, *)
extension AsyncThrowingMapSequence: AsyncSequence {
/// The type of element produced by this asynchronous sequence.
///
/// The map sequence produces whatever type of element its the transforming
/// closure produces.
public typealias Element = Transformed
/// The type of error produced by this asynchronous sequence.
///
/// The map sequence produces errors from either the base
/// sequence or the `transform` 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 map sequence.
public struct Iterator: AsyncIteratorProtocol {
@usableFromInline
var baseIterator: Base.AsyncIterator
@usableFromInline
let transform: (Base.Element) async throws -> Transformed
@usableFromInline
var finished = false
@usableFromInline
init(
_ baseIterator: Base.AsyncIterator,
transform: @escaping (Base.Element) async throws -> Transformed
) {
self.baseIterator = baseIterator
self.transform = transform
}
/// Produces the next element in the map sequence.
///
/// This iterator calls `next()` on its base iterator; if this call returns
/// `nil`, `next()` returns nil. Otherwise, `next()` returns the result of
/// calling the transforming closure on the received element. If calling
/// the closure throws an error, the sequence ends and `next()` rethrows
/// the error.
@inlinable
public mutating func next() async throws -> Transformed? {
guard !finished, let element = try await baseIterator.next() else {
return nil
}
do {
return try await transform(element)
} catch {
finished = true
throw error
}
}
/// Produces the next element in the map sequence.
///
/// This iterator calls `next(isolation:)` on its base iterator; if this
/// call returns `nil`, `next(isolation:)` returns nil. Otherwise,
/// `next(isolation:)` returns the result of calling the transforming
/// closure on the received element. If calling the closure throws an error,
/// the sequence ends and `next(isolation:)` rethrows the error.
@available(SwiftStdlib 6.0, *)
@inlinable
public mutating func next(isolation actor: isolated (any Actor)?) async throws(Failure) -> Transformed? {
guard !finished, let element = try await baseIterator.next(isolation: actor) else {
return nil
}
do {
return try await transform(element)
} catch {
finished = true
throw error
}
}
}
@inlinable
public __consuming func makeAsyncIterator() -> Iterator {
return Iterator(base.makeAsyncIterator(), transform: transform)
}
}
@available(SwiftStdlib 5.1, *)
extension AsyncThrowingMapSequence: @unchecked Sendable
where Base: Sendable,
Base.Element: Sendable,
Transformed: Sendable { }
@available(SwiftStdlib 5.1, *)
extension AsyncThrowingMapSequence.Iterator: @unchecked Sendable
where Base.AsyncIterator: Sendable,
Base.Element: Sendable,
Transformed: Sendable { }
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