Swift·Swift from optionals to SwiftUI

Closures

Pass behaviour with closure syntax and capture lists.

Beginner 12 min read Lesson 6 of 300 Challenge included

What you will be able to do

Use trailing closure syntax.
Mark escaping closures that outlive the call.
Use capture lists to avoid retain cycles.
Keep closures small.

In plain English

Closures are functions without a name. Escaping closures can outlive the call, so capture self explicitly and use weak or unowned when retaining the owner would create a cycle.

Closures.swiftSwift

func load(completion: @escaping (Result<[Lesson], Error>) -> Void) {
    // async work later
    completion(.success([]))
}

let names = [Lesson].init().map { $0.title }
print(names)

Your turn

Capture self weakly

Medium

Write a capture list for a closure that uses self weakly.

SWIFT · starter

{ self.load() }

Check your understanding before moving on.

Knowledge checkQuestion 1

Which annotation marks a closure that escapes the function?

Select an answer to continue

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Next: Concurrency

Lesson 6 of 300 · 0% of course