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Comparative
Asynchronous
Programming
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Agenda
1. Asynchronous programming is hard.
2. Swift already supports a few async methodologies.
3. Swift supports some other paradigms.
4. But lacks support for others.
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Asynchronous Programming:
Difficult and Subjective
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“Normal” programming
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let returnValue = someFunctionCall()
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Asynchronous programming
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Development is all about tradeoffs
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let file = readFile()
...
readFile() { file in
...
}
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Embrace Tradeoffs
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Swift Has Async Built-in. Sorta.
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Built-in Async Approaches
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Grand Central Dispatch
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NSOperationQueue /
DRBOperationTree
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POSIX Threads
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Target / Action
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Callbacks / Completion Handlers
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logIn(with: credentials) { result in
// Handle login success or failure
}
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Callback Hell
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getCredentialsFromUser() { credentials in
logIn(with: credentials) { result in
// Handle login success or failure
}
}
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getCredentialsFromUser() { credentials, error in
if credentials {
logIn(with: credentials) { login, error in
if login {
// Handle login success
} else {
// Handle error
}
}
} else {
// Handle error
}
}
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(credentials: Credentials?) -> Void
(credentials: Credentials?, error: Error?) -> Void
(result: Result) -> Void
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enum Result {
case success(T)
case error(Error)
}
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Callback Heaven
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Some Async Abstractions are
Supported in Swift
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Promises & Futures
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getCredentialsFromUser()
.flatMap { credentials in
return login(with: credentials)
}
.onSuccess { login in
// Handle login success
}
.onFailure { error in
// Handle login error
}
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Functional Reactive Programming
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getCredentialsFromUser()
.flatMap { credentials in
return login(with: credentials)
}
.on(next: { login in
// Handle login success
}, error: { error in
// Handle login error
})
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gerstureRecognizer.rx
.event
.map { recognizer in
return recognizer.location(in: recognizer.view)
}
.bind(to: circle.rx.center)
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Actor Model
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Actor Model
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Some Async Abstractions are
Impossible in Swift
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Async / Await
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async func logIn() -> Login {
let credentials = await getCredentialsFromUser()
return await logIn(with: credentials)
}
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Coroutines and Generator Functions
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func fibGenerator*() -> Int {
var i = 0, j = 1
repeat {
let next = i + j
yield next
(i, j) = (j, next)
} while true
}
fibGenerator() // returns 1
fibGenerator() // returns 2
fibGenerator() // returns 3
fibGenerator() // returns 5
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Wrap Up
1. There’s no “right way” to do async programming.
2. Asynchronous abstractions built into Swift aren’t great.
3. There are some cool things you can do in Swift.
4. There are other cool things that you can’t do in Swift.
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