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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
//
//===----------------------------------------------------------------------===//
/// 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`.
@inlinable
public func 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.
@frozen
public struct AsyncChain2Sequence<Base1: AsyncSequence, Base2: AsyncSequence> where Base1.Element == Base2.Element {
@usableFromInline
let base1: Base1
@usableFromInline
let base2: Base2
@usableFromInline
init(_ base1: Base1, _ base2: Base2) {
self.base1 = base1
self.base2 = base2
}
}
extension AsyncChain2Sequence: AsyncSequence {
public typealias Element = Base1.Element
/// The iterator for a `AsyncChain2Sequence` instance.
@frozen
public struct Iterator: AsyncIteratorProtocol {
@usableFromInline
var base1: Base1.AsyncIterator?
@usableFromInline
var base2: Base2.AsyncIterator?
@usableFromInline
init(_ base1: Base1.AsyncIterator, _ base2: Base2.AsyncIterator) {
self.base1 = base1
self.base2 = base2
}
@inlinable
public mutating func next() async rethrows -> Element? {
do {
if let value = try await base1?.next() {
return value
} else {
base1 = nil
}
return try await base2?.next()
} catch {
base1 = nil
base2 = nil
throw error
}
}
}
@inlinable
public func makeAsyncIterator() -> Iterator {
Iterator(base1.makeAsyncIterator(), base2.makeAsyncIterator())
}
}
extension AsyncChain2Sequence: Sendable where Base1: Sendable, Base2: Sendable { }
@available(*, unavailable)
extension AsyncChain2Sequence.Iterator: Sendable { }
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