CODEWITHSUNDEEP
swiftswift5xcode13swift-concurrency
Denis Kreshikhin
Denis Kreshikhin

Reputation: 9430

How to access an actor-isolated property

I try to check the actor's behavior. This is a new feature provided by Swift5.5.

I've created a playground with an example code from the official documentation swift.org:

    import Foundation
    
    actor TemperatureLogger {
        let label: String
        var measurements: [Int]
        private(set) var max: Int

        init(label: String, measurement: Int) {
            self.label = label
            self.measurements = [measurement]
            self.max = measurement
        }
    }

    let logger = TemperatureLogger(label: "Outdoors", measurement: 25)
    print(await logger.max)
    // Prints "25"

But my compiler fails on this example:

errors

Swift Compiler Error:

'await' in a function that does not support concurrency

Actor-isolated property 'max' can only be referenced from inside the actor

So how to access an actor-isolated property?

Maybe it's a bug in the compiler or in the example code?

Xcode Version 13.0 beta (13A5154h) Swift Version 5.5

Upvotes: 25

Views: 33257

Answers (1)

Bradley Mackey
Bradley Mackey

Reputation: 7708

Put the access in an Task block. Actor isolated properties synchronise and enforce exclusive access through the "cooperative thread pool" and could suspend, so this needs to run asynchronously.

let logger = TemperatureLogger(label: "Outdoors", measurement: 25)
Task {
    print(await logger.max)
    // Prints "25"
}

Upvotes: 25

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