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//===----------------------------------------------------------------------===//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2021 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
// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
//
//===----------------------------------------------------------------------===//
import Swift
@available(SwiftStdlib 5.1, *)
extension AsyncSequence {
/// Creates an asynchronous sequence that contains, in order, the elements of
/// the base sequence that satisfy the given predicate.
///
/// In this example, an asynchronous sequence called `Counter` produces `Int`
/// values from `1` to `10`. The `filter(_:)` method returns `true` for even
/// values and `false` for odd values, thereby filtering out the odd values:
///
/// let stream = Counter(howHigh: 10)
/// .filter { $0 % 2 == 0 }
/// for await number in stream {
/// print(number, terminator: " ")
/// }
/// // Prints "2 4 6 8 10 "
///
/// - Parameter isIncluded: A closure that takes an element of the
/// asynchronous sequence as its argument and returns a Boolean value
/// that indicates whether to include the element in the filtered sequence.
/// - Returns: An asynchronous sequence that contains, in order, the elements
/// of the base sequence that satisfy the given predicate.
@preconcurrency
@inlinable
public __consuming func filter(
_ isIncluded: @Sendable @escaping (Element) async -> Bool
) -> AsyncFilterSequence<Self> {
return AsyncFilterSequence(self, isIncluded: isIncluded)
}
}
/// An asynchronous sequence that contains, in order, the elements of
/// the base sequence that satisfy a given predicate.
@available(SwiftStdlib 5.1, *)
public struct AsyncFilterSequence<Base: AsyncSequence> {
@usableFromInline
let base: Base
@usableFromInline
let isIncluded: (Element) async -> Bool
@usableFromInline
init(
_ base: Base,
isIncluded: @escaping (Base.Element) async -> Bool
) {
self.base = base
self.isIncluded = isIncluded
}
}
@available(SwiftStdlib 5.1, *)
extension AsyncFilterSequence: AsyncSequence {
/// The type of element produced by this asynchronous sequence.
///
/// The filter sequence produces whatever type of element its base
/// sequence produces.
public typealias Element = Base.Element
/// The type of the error that can be produced by the sequence.
///
/// The filter sequence produces whatever type of error its
/// base sequence does.
@available(SwiftStdlib 6.0, *)
public typealias Failure = Base.Failure
/// The type of iterator that produces elements of the sequence.
public typealias AsyncIterator = Iterator
/// The iterator that produces elements of the filter sequence.
public struct Iterator: AsyncIteratorProtocol {
// FIXME: Remove when $AssociatedTypeImplements is no longer needed
@available(SwiftStdlib 6.0, *)
public typealias Failure = Base.Failure
@usableFromInline
var baseIterator: Base.AsyncIterator
@usableFromInline
let isIncluded: (Base.Element) async -> Bool
@usableFromInline
init(
_ baseIterator: Base.AsyncIterator,
isIncluded: @escaping (Base.Element) async -> Bool
) {
self.baseIterator = baseIterator
self.isIncluded = isIncluded
}
/// Produces the next element in the filter sequence.
///
/// This iterator calls `next()` on its base iterator; if this call returns
/// `nil`, `next()` returns nil. Otherwise, `next()` evaluates the
/// result with the `predicate` closure. If the closure returns `true`,
/// `next()` returns the received element; otherwise it awaits the next
/// element from the base iterator.
@inlinable
public mutating func next() async rethrows -> Base.Element? {
while true {
guard let element = try await baseIterator.next() else {
return nil
}
if await isIncluded(element) {
return element
}
}
}
/// Produces the next element in the filter sequence.
///
/// This iterator calls `next(isolation:)` on its base iterator; if this
/// call returns `nil`, `next(isolation:)` returns nil. Otherwise,
/// `next(isolation:)` evaluates the result with the `predicate` closure. If
/// the closure returns `true`, `next(isolation:)` returns the received
/// element; otherwise it awaits the next element from the base iterator.
@available(SwiftStdlib 6.0, *)
@inlinable
public mutating func next(isolation actor: isolated (any Actor)?) async throws(Failure) -> Base.Element? {
while true {
guard let element = try await baseIterator.next(isolation: actor) else {
return nil
}
if await isIncluded(element) {
return element
}
}
}
}
@inlinable
public __consuming func makeAsyncIterator() -> Iterator {
return Iterator(base.makeAsyncIterator(), isIncluded: isIncluded)
}
}
@available(SwiftStdlib 5.1, *)
extension AsyncFilterSequence: @unchecked Sendable
where Base: Sendable,
Base.Element: Sendable { }
@available(SwiftStdlib 5.1, *)
extension AsyncFilterSequence.Iterator: @unchecked Sendable
where Base.AsyncIterator: Sendable,
Base.Element: Sendable { }
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