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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 with a separator.
@inlinable
public func joined<Separator: AsyncSequence>(separator: Separator) -> AsyncJoinedBySeparatorSequence<Self, Separator> {
return AsyncJoinedBySeparatorSequence(self, separator: separator)
}
}
/// An `AsyncSequence` that concatenates `AsyncSequence` elements with a separator.
public struct AsyncJoinedBySeparatorSequence<Base: AsyncSequence, Separator: AsyncSequence>: AsyncSequence where Base.Element: AsyncSequence, Separator.Element == Base.Element.Element {
public typealias Element = Base.Element.Element
public typealias AsyncIterator = Iterator
/// The iterator for an `AsyncJoinedBySeparatorSequence` instance.
public struct Iterator: AsyncIteratorProtocol {
@usableFromInline
enum State {
@usableFromInline
enum SeparatorState {
case initial(Separator)
case partialAsync(Separator.AsyncIterator, ContiguousArray<Element>)
case cached(ContiguousArray<Element>)
case partialCached(ContiguousArray<Element>.Iterator, ContiguousArray<Element>)
@usableFromInline
func startSeparator() -> SeparatorState {
switch self {
case .initial(let separatorSequence):
return .partialAsync(separatorSequence.makeAsyncIterator(), [])
case .cached(let array):
return .partialCached(array.makeIterator(), array)
default:
fatalError("Invalid separator sequence state")
}
}
@usableFromInline
func next() async rethrows -> (Element?, SeparatorState) {
switch self {
case .partialAsync(var separatorIterator, var cache):
guard let next = try await separatorIterator.next() else {
return (nil, .cached(cache))
}
cache.append(next)
return (next, .partialAsync(separatorIterator, cache))
case .partialCached(var cacheIterator, let cache):
guard let next = cacheIterator.next() else {
return (nil, .cached(cache))
}
return (next, .partialCached(cacheIterator, cache))
default:
fatalError("Invalid separator sequence state")
}
}
}
case initial(Base.AsyncIterator, Separator)
case sequence(Base.AsyncIterator, Base.Element.AsyncIterator, SeparatorState)
case separator(Base.AsyncIterator, SeparatorState, Base.Element)
case terminal
}
@usableFromInline
var state: State
@usableFromInline
init(_ iterator: Base.AsyncIterator, separator: Separator) {
state = .initial(iterator, separator)
}
@inlinable
public mutating func next() async rethrows -> Base.Element.Element? {
do {
switch state {
case .terminal:
return nil
case .initial(var outerIterator, let separator):
guard let innerSequence = try await outerIterator.next() else {
state = .terminal
return nil
}
let innerIterator = innerSequence.makeAsyncIterator()
state = .sequence(outerIterator, innerIterator, .initial(separator))
return try await next()
case .sequence(var outerIterator, var innerIterator, let separatorState):
if let item = try await innerIterator.next() {
state = .sequence(outerIterator, innerIterator, separatorState)
return item
}
guard let nextInner = try await outerIterator.next() else {
state = .terminal
return nil
}
state = .separator(outerIterator, separatorState.startSeparator(), nextInner)
return try await next()
case .separator(let iterator, let separatorState, let nextBase):
let (itemOpt, newSepState) = try await separatorState.next()
guard let item = itemOpt else {
state = .sequence(iterator, nextBase.makeAsyncIterator(), newSepState)
return try await next()
}
state = .separator(iterator, newSepState, nextBase)
return item
}
} catch {
state = .terminal
throw error
}
}
}
@usableFromInline
let base: Base
@usableFromInline
let separator: Separator
@usableFromInline
init(_ base: Base, separator: Separator) {
self.base = base
self.separator = separator
}
@inlinable
public func makeAsyncIterator() -> Iterator {
return Iterator(base.makeAsyncIterator(), separator: separator)
}
}
extension AsyncJoinedBySeparatorSequence: Sendable
where Base: Sendable, Base.Element: Sendable, Base.Element.Element: Sendable, Separator: Sendable { }
@available(*, unavailable)
extension AsyncJoinedBySeparatorSequence.Iterator: Sendable { }
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