Modern Concurrency: Beyond the Basics

Oct 20 2022 · Swift 5.5, iOS 15, Xcode 13.4

Part 1: AsyncStream & Continuations

05. Using a Buffered AsyncStream

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Previous episode: 04. Using AsyncStream for Notifications Next episode: 06. Unit Testing

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Notes: 05. Using a Buffered AsyncStream

Use Xcode 13 for this exercise. Xcode 14 beta uses Swift 6, which doesn’t allow using countdown in the scheduledTRimer closure.

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Your challenge is to rewrite countdown to using the buffered, push-based version of AsyncStream. (upbeat music) Use Timer instead of Task.sleep to wait one second between messages. The starter project already has code for Timer.scheduledTimer that fires every second. Inside the scheduledTimer closure, yield the correct message when countdown is 3, 2, 1, and 0. Remember to decrement countdown after yielding 3, 2, and 1. When countdown is 0, return the user's message, invalidate the timer, and finish the continuation. Good luck. (casual music) Welcome back. Hopefully, you had success with this task. Here's how I did it. In BlabberModel, countdown to already has starter code to create a timer that fires each second. Instead of the pull-based AsyncStream code you wrote in Episode 3, inside the Timer closure, I first handled the countdown digits. On every timer tick, I called yield on the continuation to produce the countdown value and then decreased countdown. Next, I needed to add code for when countdown reaches 0. I did this before continuation.yield. When countdown reaches 0, I stopped the timer, yield the user's message, and call continuation.finish to complete the sequence. Actually, there's a shortcut to produce the last value and complete the sequence at the same time. And to show it works. The next episode is about unit testing.