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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
//
//===----------------------------------------------------------------------===//
/// Creates an asynchronous sequence that combines the latest values from three `AsyncSequence` types
/// by emitting a tuple of the values. ``combineLatest(_:_:_:)`` only emits a value whenever any of the base `AsyncSequence`s
/// emit a value (so long as each of the bases have emitted at least one value).
///
/// Finishes:
/// ``combineLatest(_:_:_:)`` finishes when one of the bases finishes before emitting any value or
/// when all bases finished.
///
/// Throws:
/// ``combineLatest(_:_:_:)`` throws when one of the bases throws. If one of the bases threw any buffered and not yet consumed
/// values will be dropped.
public func combineLatest<
Base1: AsyncSequence,
Base2: AsyncSequence,
Base3: AsyncSequence
>(_ base1: Base1, _ base2: Base2, _ base3: Base3) -> AsyncCombineLatest3Sequence<Base1, Base2, Base3> where
Base1: Sendable,
Base1.Element: Sendable,
Base2: Sendable,
Base2.Element: Sendable,
Base3: Sendable,
Base3.Element: Sendable {
AsyncCombineLatest3Sequence(base1, base2, base3)
}
/// An `AsyncSequence` that combines the latest values produced from three asynchronous sequences into an asynchronous sequence of tuples.
public struct AsyncCombineLatest3Sequence<
Base1: AsyncSequence,
Base2: AsyncSequence,
Base3: AsyncSequence
>: AsyncSequence, Sendable where
Base1: Sendable,
Base1.Element: Sendable,
Base2: Sendable,
Base2.Element: Sendable,
Base3: Sendable,
Base3.Element: Sendable {
public typealias Element = (Base1.Element, Base2.Element, Base3.Element)
public typealias AsyncIterator = Iterator
let base1: Base1
let base2: Base2
let base3: Base3
init(_ base1: Base1, _ base2: Base2, _ base3: Base3) {
self.base1 = base1
self.base2 = base2
self.base3 = base3
}
public func makeAsyncIterator() -> AsyncIterator {
Iterator(storage: .init(self.base1, self.base2, self.base3)
)
}
public struct Iterator: AsyncIteratorProtocol {
final class InternalClass {
private let storage: CombineLatestStorage<Base1, Base2, Base3>
fileprivate init(storage: CombineLatestStorage<Base1, Base2, Base3>) {
self.storage = storage
}
deinit {
self.storage.iteratorDeinitialized()
}
func next() async rethrows -> Element? {
guard let element = try await self.storage.next() else {
return nil
}
// This force unwrap is safe since there must be a third element.
return (element.0, element.1, element.2!)
}
}
let internalClass: InternalClass
fileprivate init(storage: CombineLatestStorage<Base1, Base2, Base3>) {
self.internalClass = InternalClass(storage: storage)
}
public mutating func next() async rethrows -> Element? {
try await self.internalClass.next()
}
}
}
@available(*, unavailable)
extension AsyncCombineLatest3Sequence.Iterator: Sendable { }
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