Intersperse

Places a given value in between each element of the asynchronous sequence.

[Source | Tests]

let numbers = [1, 2, 3].async.interspersed(with: 0)
for await number in numbers {
  print(number)
}
// prints 1 0 2 0 3

let empty = [].async.interspersed(with: 0)
// await Array(empty) == []

interspersed(with:) takes a separator value and inserts it in between every element in the asynchronous sequence.

Detailed Design

A new method is added to AsyncSequence:

extension AsyncSequence {
  func interspersed(with separator: Element) -> AsyncInterspersedSequence<Self>
}

The new AsyncInterspersedSequence type represents the asynchronous sequence when the separator is inserted between each element.

When the base asynchronous sequence can throw on iteration, AsyncInterspersedSequence will throw on iteration. When the base does not throw, the iteration of AsyncInterspersedSequence does not throw either.

AsyncInterspersedSequence is conditionally Sendable when the base asynchronous sequence is Sendable and the element is also Sendable.

Naming

This method’s and type’s name match the term of art used in other languages and libraries.

This method is a direct analog to the synchronous version defined in the Swift Algorithms package.

Comparison with other languages

Haskell: Has an intersperse function which takes an element and a list and 'intersperses' that element between the elements of the list.

Rust: Has a function called intersperse to insert a particular value between each element.