Created
September 17, 2022 04:47
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| extension AsyncSequence where Element: Hashable { | |
| /// Sequence that emits unique elements once each | |
| func unique() -> AsyncUniqueSequence<Self> { | |
| AsyncUniqueSequence(self) | |
| } | |
| } | |
| /// Sequence that only emits unique elements once. | |
| /// While iterating, all emitted elements are retained within a `Set` to ensure uniqueness of each element emitted. | |
| struct AsyncUniqueSequence<Base>: AsyncSequence where Base: AsyncSequence, Base.Element: Hashable { | |
| typealias Element = Base.Element | |
| private let base: Base | |
| init(_ base: Base) { | |
| self.base = base | |
| } | |
| func makeAsyncIterator() -> AsyncIterator { | |
| AsyncIterator(base.makeAsyncIterator()) | |
| } | |
| struct AsyncIterator: AsyncIteratorProtocol { | |
| private var iterator: Base.AsyncIterator | |
| private var elements: Set<Base.Element> | |
| init(_ iterator: Base.AsyncIterator) { | |
| self.iterator = iterator | |
| self.elements = [] | |
| } | |
| mutating func next() async throws -> Base.Element? { | |
| while let element = try await iterator.next() { | |
| if !elements.contains(element) { | |
| elements.insert(element) | |
| return element | |
| } | |
| } | |
| return nil | |
| } | |
| } | |
| } |
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