When should I use assumeIsolated instead of Task?

Use assumeIsolated when you are already on the correct executor and need synchronous access. Use Task for deferred, asynchronous work from a different context.

Is @preconcurrency the same as assumeIsolated?

In the context of protocol conformance, @preconcurrency acts as a shorthand that automatically wraps callback logic in an assumeIsolated-like check for the main actor.

How does this skill improve Swift unit testing?

It allows you to verify and test MainActor-isolated logic synchronously, which eliminates the need for async expectations and makes tests faster and more reliable.

Does assumeIsolated prevent runtime crashes?

No, assumeIsolated will intentionally crash if called from the wrong isolation domain. This is a safety feature designed to prevent data races and memory corruption.

Swift Actor Isolation Guard

Name: Swift Actor Isolation Guard
Author: CharlesWiltgen

byCharlesWiltgen

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233

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Mobile Development

Guides developers in using synchronous actor access and assumeIsolated patterns for Swift concurrency.

This skill provides specialized implementation patterns and best practices for managing Swift actor isolation domains synchronously. It focuses on the assumeIsolated API, enabling developers to access actor-isolated state without the overhead of asynchronous hops in performance-critical code, unit tests, and legacy delegate callbacks. By clarifying the differences between Task-based execution and synchronous isolation checks, it helps prevent common concurrency pitfalls and ensures thread safety in modern xOS application development.

主な機能

01Detailed safety checks and crash behavior documentation

02Performance optimization tips for avoiding unnecessary async hops

03Implementation patterns for MainActor.assumeIsolated and custom actors

04Guidance on @preconcurrency protocol conformances and legacy delegates

05Synchronous unit testing strategies for actor-isolated code

06233 GitHub stars

ユースケース

01Testing MainActor ViewModels synchronously to avoid Task overhead and flakiness

02Optimizing high-frequency code paths that require synchronous access to protected actor state

03Interfacing with legacy UIKit or CoreLocation delegates guaranteed to run on the main thread

主な機能

01Detailed safety checks and crash behavior documentation

02Performance optimization tips for avoiding unnecessary async hops

03Implementation patterns for MainActor.assumeIsolated and custom actors

04Guidance on @preconcurrency protocol conformances and legacy delegates

05Synchronous unit testing strategies for actor-isolated code

06233 GitHub stars

ユースケース

01Testing MainActor ViewModels synchronously to avoid Task overhead and flakiness

02Optimizing high-frequency code paths that require synchronous access to protected actor state

03Interfacing with legacy UIKit or CoreLocation delegates guaranteed to run on the main thread