AsyncMerge2Sequence.swift

//===----------------------------------------------------------------------===//
//
// 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
@available(AsyncAlgorithms 1.0,*)
publicfunc merge<Base1:AsyncSequence, Base2:AsyncSequence>(
 _ base1:Base1,
 _ base2:Base2
)->AsyncMerge2Sequence<Base1,Base2>
where
 Base1.Element ==Base2.Element,
 Base1:Sendable,
 Base2:Sendable,
 Base1.Element:Sendable
{
returnAsyncMerge2Sequence(base1, base2)
}

/// An `AsyncSequence` that takes two upstream `AsyncSequence`s and combines their elements.
@available(AsyncAlgorithms 1.0,*)
publicstructAsyncMerge2Sequence<
 Base1:AsyncSequence,
 Base2:AsyncSequence
>:Sendable
where
 Base1.Element ==Base2.Element,
 Base1:Sendable,
 Base2:Sendable,
 Base1.Element:Sendable
{
publictypealiasElement=Base1.Element

privateletbase1:Base1
privateletbase2:Base2

 /// Initializes a new ``AsyncMerge2Sequence``.
 ///
 /// - Parameters:
 /// - base1: The first upstream ``Swift/AsyncSequence``.
 /// - base2: The second upstream ``Swift/AsyncSequence``.
init(
 _ base1:Base1,
 _ base2:Base2
){
self.base1 = base1
self.base2 = base2
}
}

@available(AsyncAlgorithms 1.0,*)
extensionAsyncMerge2Sequence:AsyncSequence{
@available(AsyncAlgorithms 1.0,*)
publicfunc makeAsyncIterator()->Iterator{
letstorage=MergeStorage<Base1,Base2,Base1>(
 base1: base1,
 base2: base2,
 base3:nil
)
returnIterator(storage: storage)
}
}

@available(AsyncAlgorithms 1.0,*)
extensionAsyncMerge2Sequence{
@available(AsyncAlgorithms 1.0,*)
publicstructIterator: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.
finalclassInternalClass:Sendable{
privateletstorage:MergeStorage<Base1,Base2,Base1>

fileprivateinit(storage:MergeStorage<Base1,Base2,Base1>){
self.storage = storage
}

deinit{
self.storage.iteratorDeinitialized()
}

func next()asyncrethrows->Element?{
tryawait storage.next()
}
}

letinternalClass:InternalClass

fileprivateinit(storage:MergeStorage<Base1,Base2,Base1>){
 internalClass =InternalClass(storage: storage)
}

publicmutatingfunc next()asyncrethrows->Element?{
tryawait internalClass.next()
}
}
}

@available(*, unavailable)
extensionAsyncMerge2Sequence.Iterator:Sendable{}