AsyncCombineLatest3Sequence.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
//
//===----------------------------------------------------------------------===//

/// 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.
@available(AsyncAlgorithms 1.0,*)
publicfunc 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.
@available(AsyncAlgorithms 1.0,*)
publicstructAsyncCombineLatest3Sequence<
 Base1:AsyncSequence,
 Base2:AsyncSequence,
 Base3:AsyncSequence
>:AsyncSequence,Sendable
where
 Base1:Sendable,
 Base1.Element:Sendable,
 Base2:Sendable,
 Base2.Element:Sendable,
 Base3:Sendable,
 Base3.Element:Sendable
{
publictypealiasElement=(Base1.Element,Base2.Element,Base3.Element)
publictypealiasAsyncIterator=Iterator

letbase1:Base1
letbase2:Base2
letbase3:Base3

init(_ base1:Base1, _ base2:Base2, _ base3:Base3){
self.base1 = base1
self.base2 = base2
self.base3 = base3
}

publicfunc makeAsyncIterator()->AsyncIterator{
Iterator(
 storage:.init(self.base1,self.base2,self.base3)
)
}

publicstructIterator:AsyncIteratorProtocol{
finalclassInternalClass{
privateletstorage:CombineLatestStorage<Base1,Base2,Base3>

fileprivateinit(storage:CombineLatestStorage<Base1,Base2,Base3>){
self.storage = storage
}

deinit{
self.storage.iteratorDeinitialized()
}

func next()asyncrethrows->Element?{
guardlet element =tryawaitself.storage.next()else{
returnnil
}

 // This force unwrap is safe since there must be a third element.
return(element.0, element.1, element.2!)
}
}

letinternalClass:InternalClass

fileprivateinit(storage:CombineLatestStorage<Base1,Base2,Base3>){
self.internalClass =InternalClass(storage: storage)
}

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

@available(*, unavailable)
extensionAsyncCombineLatest3Sequence.Iterator:Sendable{}