Default Actor Isolation

Using Swift
1

Hi,

I have an Xcode project which has 2 targets

  • TargetA - Default actor isolation is Main Actor
  • TargetB - Default actor isolation is nonisolated

Things were ok

  • Then I moved a Car.swift from TargetB to TargetA folder
  • Then I added TargetA to Car.swift
  • Now Car.swift is added to both TargetA and TargetB

I got some compilation errors relating main actor isolation which I managed to resolve, but I have some questions.

Questions

  1. Is Car main actor isolated or non isolated?
  2. Is there a way to see which files are default main actor isolated?
  3. If a synchronous function is marked as nonisloated then will it continue to run in the same thread as the caller?
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2

Is Car main actor isolated or non isolated?

The copy of Car in TargetA it is MainActor, and the copy in TargetB it is nonisolated. It cannot be just one, because there are two copies in two different modules that are configured to use different modes.

Is there a way to see which files are default main actor isolated?

It has been discussed a bunch, but as far as I know default isolation is not yet configurable on a per-file basis. It is defined per-module only. So, every file in a module with default main actor will use that mode.

If a synchronous function is marked as nonisolated then will it continue to run in the same thread as the caller?

Yes. This is true independent of isolation mode. Just for sake of completeness, this is also true for asynchronous functions if NonisolatedNonsendingByDefault is enabled.

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3

Thanks a lot @mattie

To resolve the error, I made them nonisolated as there were stateless struct and had only synchronous functions.

That makes sense, may be I will try with a smaller POC to check this.

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