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Conversion from `@isolated(any)` function type to synchronous function type (ConversionFromIsolatedAnyToSynchronous)

Overview

A function value with type @isolated(any) carries its actor isolation dynamically. Calling such a function from a context that does not share its isolation requires hopping to the function’s actor, which can only be done from an asynchronous context. As a result, an @isolated(any) function value cannot be converted to a synchronous, non-@isolated(any) function type.

@MainActor func updateUI() { /* ... */ }

func runInBackground(_ work: @escaping @Sendable () -> ()) {
  DispatchQueue.global().async { work() }
}

func schedule(_ work: @escaping @isolated(any) @Sendable () -> ()) {
  runInBackground(work) // warning: converting @isolated(any) function of type '@isolated(any) @Sendable () -> ()' to synchronous function type '@Sendable () -> ()' is not allowed
}

schedule(updateUI)

In the example, updateUI() would run on a background thread instead of the main actor which could result in a data race.

This conversion is currently diagnosed as a warning that will become an error in a future Swift language mode. To opt in to treating it as an error today, pass -Werror ConversionFromIsolatedAnyToSynchronous.

To resolve the diagnostic, convert the function value to an async function type and use await when invoking the function, or remove the @isolated(any) attribute from the source type if it is not needed.

See Also