Possible to return an AsyncSequence<T> for iOS 17 when building against iOS 18?

kabiroberai · December 19, 2024, 8:21pm

Already shared this with @joshw on Slack (we work together) but for visibility I thought I'd point out that swift-nio has a nice AnyAsyncSequence type that can do the trick. Though folks have pointed out in the past that this can have sizable perf tradeoffs so probably best used sparingly.

github.com

apple/swift-nio/blob/56f9b7c6fc9525ba36236dbb151344f8c35288df/Sources/NIOFileSystem/Internal/BufferedOrAnyStream.swift#L72


      
                      self = .bufferedStream(iterator)
                  }
          
                  internal init(wrapping iterator: AnyAsyncSequence<Element>.AsyncIterator) {
                      self = .anyAsyncSequence(iterator)
                  }
              }
          }
          
          @available(macOS 10.15, iOS 13.0, watchOS 6.0, tvOS 13.0, *)
          internal struct AnyAsyncSequence<Element>: AsyncSequence {
              private let _makeAsyncIterator: () -> AsyncIterator
          
              internal init<S: AsyncSequence>(wrapping sequence: S) where S.Element == Element {
                  self._makeAsyncIterator = {
                      AsyncIterator(wrapping: sequence.makeAsyncIterator())
                  }
              }
          
              internal func makeAsyncIterator() -> AsyncIterator {
                  self._makeAsyncIterator()