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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
//
//===----------------------------------------------------------------------===//
import DequeModule
/// Creates an asynchronous sequence of elements from two underlying asynchronous sequences
public func merge<
Base1: AsyncSequence,
Base2: AsyncSequence,
Base3: AsyncSequence
>(_ base1: Base1, _ base2: Base2, _ base3: Base3) -> AsyncMerge3Sequence<Base1, Base2, Base3>
where
Base1.Element == Base2.Element,
Base1.Element == Base3.Element,
Base1: Sendable, Base2: Sendable, Base3: Sendable,
Base1.Element: Sendable
{
return AsyncMerge3Sequence(base1, base2, base3)
}
/// An ``Swift/AsyncSequence`` that takes three upstream ``Swift/AsyncSequence``s and combines their elements.
public struct AsyncMerge3Sequence<
Base1: AsyncSequence,
Base2: AsyncSequence,
Base3: AsyncSequence
>: Sendable where
Base1.Element == Base2.Element,
Base1.Element == Base3.Element,
Base1: Sendable, Base2: Sendable, Base3: Sendable,
Base1.Element: Sendable
{
public typealias Element = Base1.Element
private let base1: Base1
private let base2: Base2
private let base3: Base3
/// Initializes a new ``AsyncMerge2Sequence``.
///
/// - Parameters:
/// - base1: The first upstream ``Swift/AsyncSequence``.
/// - base2: The second upstream ``Swift/AsyncSequence``.
/// - base3: The third upstream ``Swift/AsyncSequence``.
init(
_ base1: Base1,
_ base2: Base2,
_ base3: Base3
) {
self.base1 = base1
self.base2 = base2
self.base3 = base3
}
}
extension AsyncMerge3Sequence: AsyncSequence {
public func makeAsyncIterator() -> Iterator {
let storage = MergeStorage(
base1: base1,
base2: base2,
base3: base3
)
return Iterator(storage: storage)
}
}
public extension AsyncMerge3Sequence {
struct Iterator: AsyncIteratorProtocol {
/// This class is needed to hook the deinit to observe once all references to the ``AsyncIterator`` are dropped.
///
/// If we get move-only types we should be able to drop this class and use the `deinit` of the ``AsyncIterator`` struct itself.
final class InternalClass: Sendable {
private let storage: MergeStorage<Base1, Base2, Base3>
fileprivate init(storage: MergeStorage<Base1, Base2, Base3>) {
self.storage = storage
}
deinit {
self.storage.iteratorDeinitialized()
}
func next() async rethrows -> Element? {
try await storage.next()
}
}
let internalClass: InternalClass
fileprivate init(storage: MergeStorage<Base1, Base2, Base3>) {
internalClass = InternalClass(storage: storage)
}
public mutating func next() async rethrows -> Element? {
try await internalClass.next()
}
}
}
@available(*, unavailable)
extension AsyncMerge3Sequence.Iterator: Sendable { }
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