Updated for Xcode 15
Swift does not provide a built-in way of converting an AsyncSequence
into a regular Sequence
, but often you’ll want to make this conversion yourself so you don’t need to keep awaiting results to come back in the future.
The easiest thing to do is call reduce(into:)
on the sequence, appending each item to an array of the sequence’s element type. To make this more reusable, I’d recommend adding an extension such as this one:
extension AsyncSequence {
func collect() async rethrows -> [Element] {
try await reduce(into: [Element]()) { $0.append($1) }
}
}
With that in place, you can now call collect()
on any async sequence in order to get a simple array of its values. Because this is an async operation, you must call it using await
like so:
extension AsyncSequence {
func collect() async rethrows -> [Element] {
try await reduce(into: [Element]()) { $0.append($1) }
}
}
func getNumberArray() async throws -> [Int] {
let url = URL(string: "https://hws.dev/random-numbers.txt")!
let numbers = url.lines.compactMap(Int.init)
return try await numbers.collect()
}
if let numbers = try? await getNumberArray() {
for number in numbers {
print(number)
}
}
Download this as an Xcode project
Tip: Because we’ve made collect()
use rethrows
, you only need to call it using try
if the call to reduce()
would normally throw, so if you have an async sequence that doesn’t throw errors you can skip try
entirely.
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