Cleaning up Async Without Swift 5.5 — Figure
It’s finally here! After seven years of callbacks and completion handlers, we now have a way to cleanly and correctly make asynchronous calls in Swift without endless nesting. It's async/await and it’s awesome.
For those of us supporting older deployment targets, this can be a bit of a let down. But not all hope is lost! We can build clean, flattened-out async handling on our own. And maybe learn a thing or two about the nature of asynchrony along the way?
This works, but execution jumps all over the place spatially and temporally making the code hard to reason about and prone to errors. We would like to specify our async calls procedurally, instead. One right after the other, no nesting.
Long time readers will recognize this as a coroutine. A coroutine is ideal for handling asynchronous work because we can suspend it just after it begins its async job, then resume it again right where it left off when the job completes and we're ready to continue.
This flow of events might sound familiar. Let’s look a little closer look at the execution of a standard “completion handler” function:
