AsyncChain2Sequence.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
//
//===----------------------------------------------------------------------===//

/// Returns a new asynchronous sequence that iterates over the two given asynchronous sequences, one
/// followed by the other.
///
/// - Parameters:
/// - s1: The first asynchronous sequence.
/// - s2: The second asynchronous sequence.
/// - Returns: An asynchronous sequence that iterates first over the elements of `s1`, and
/// then over the elements of `s2`.
@available(AsyncAlgorithms 1.0,*)
@inlinable
publicfunc chain<Base1:AsyncSequence, Base2:AsyncSequence>(
 _ s1:Base1,
 _ s2:Base2
)->AsyncChain2Sequence<Base1,Base2>where Base1.Element ==Base2.Element{
AsyncChain2Sequence(s1, s2)
}

/// A concatenation of two asynchronous sequences with the same element type.
@available(AsyncAlgorithms 1.0,*)
@frozen
publicstructAsyncChain2Sequence<Base1:AsyncSequence, Base2:AsyncSequence>where Base1.Element ==Base2.Element{
@usableFromInline
letbase1:Base1

@usableFromInline
letbase2:Base2

@usableFromInline
init(_ base1:Base1, _ base2:Base2){
self.base1 = base1
self.base2 = base2
}
}

@available(AsyncAlgorithms 1.0,*)
extensionAsyncChain2Sequence:AsyncSequence{
publictypealiasElement=Base1.Element

 /// The iterator for a `AsyncChain2Sequence` instance.
@available(AsyncAlgorithms 1.0,*)
@frozen
publicstructIterator:AsyncIteratorProtocol{
@usableFromInline
varbase1:Base1.AsyncIterator?

@usableFromInline
varbase2:Base2.AsyncIterator?

@usableFromInline
init(_ base1:Base1.AsyncIterator, _ base2:Base2.AsyncIterator){
self.base1 = base1
self.base2 = base2
}

@inlinable
publicmutatingfunc next()asyncrethrows->Element?{
do{
iflet value =tryawait base1?.next(){
return value
} else {
 base1 =nil
}
returntryawait base2?.next()
}catch{
 base1 =nil
 base2 =nil
throw error
}
}
}

@available(AsyncAlgorithms 1.0,*)
@inlinable
publicfunc makeAsyncIterator()->Iterator{
Iterator(base1.makeAsyncIterator(), base2.makeAsyncIterator())
}
}

@available(AsyncAlgorithms 1.0,*)
extensionAsyncChain2Sequence:Sendablewhere Base1:Sendable, Base2:Sendable{}

@available(*, unavailable)
extensionAsyncChain2Sequence.Iterator:Sendable{}