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//===----------------------------------------------------------------------===//
//
// This source file is part of the Swift Async Algorithms open source project
//
// Copyright (c) 2022 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
//
//===----------------------------------------------------------------------===//
extension AsyncSequence where Element: AsyncSequence {
/// Concatenate an `AsyncSequence` of `AsyncSequence` elements
@inlinable
public func joined() -> AsyncJoinedSequence<Self> {
return AsyncJoinedSequence(self)
}
}
/// An `AsyncSequence` that concatenates`AsyncSequence` elements
@frozen
public struct AsyncJoinedSequence<Base: AsyncSequence>: AsyncSequence where Base.Element: AsyncSequence {
public typealias Element = Base.Element.Element
public typealias AsyncIterator = Iterator
/// The iterator for an `AsyncJoinedSequence` instance.
@frozen
public struct Iterator: AsyncIteratorProtocol {
@usableFromInline
enum State {
case initial(Base.AsyncIterator)
case sequence(Base.AsyncIterator, Base.Element.AsyncIterator)
case terminal
}
@usableFromInline
var state: State
@inlinable
init(_ iterator: Base.AsyncIterator) {
state = .initial(iterator)
}
@inlinable
public mutating func next() async rethrows -> Base.Element.Element? {
do {
switch state {
case .terminal:
return nil
case .initial(var outerIterator):
guard let innerSequence = try await outerIterator.next() else {
state = .terminal
return nil
}
let innerIterator = innerSequence.makeAsyncIterator()
state = .sequence(outerIterator, innerIterator)
return try await next()
case .sequence(var outerIterator, var innerIterator):
if let item = try await innerIterator.next() {
state = .sequence(outerIterator, innerIterator)
return item
}
guard let nextInner = try await outerIterator.next() else {
state = .terminal
return nil
}
state = .sequence(outerIterator, nextInner.makeAsyncIterator())
return try await next()
}
} catch {
state = .terminal
throw error
}
}
}
@usableFromInline
let base: Base
@usableFromInline
init(_ base: Base) {
self.base = base
}
@inlinable
public func makeAsyncIterator() -> Iterator {
return Iterator(base.makeAsyncIterator())
}
}
extension AsyncJoinedSequence: Sendable
where Base: Sendable, Base.Element: Sendable, Base.Element.Element: Sendable { }
@available(*, unavailable)
extension AsyncJoinedSequence.Iterator: Sendable { }
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