Swift 6 - Switch from @MainActor func to async function

Question

How can I call in Swift 6 a normal async function from a MainActor function? I do not want to execute URLRequests on the MainThread

I want to switch from the Main Thread to an async Thread but I have no idea how to do it... This code doesn't work and throws the following error: Sending 'self.service' risks causing data races

import SwiftUI

struct CustomView: View {
    private let viewModel: CustomViewModel = CustomViewModel()

    var body: some View {
        Text("HELLO")
            .task {
                Task {
                    await viewModel.getDataFromBackend()
                }
            }
    }
}

@Observable
final class CustomViewModel {
    private let service: CustomService = DefaultCustomService()

    @MainActor func getDataFromBackend() async {
        // Updating UI on Main-Thread

        // This shouldn't run on the Main Thread!
        await service.provideBackendData()
    }
}


protocol CustomService {
    func provideBackendData() async
}

struct DefaultCustomService: CustomService {
    func provideBackendData() async {
        // Async Stuff which shouldn't run on Main-Thread
    }
}

Answer 1

You can just add

protocol CustomService: Sendable {

To remove the error.

In order to safely make something Sendable you should meet all of these official requirements

• Value types
• Reference types with no mutable storage
• Reference types that internally manage access to their state
• Functions and closures (by marking them with @Sendable)

https://developer.apple.com/documentation/swift/sendable

Unofficially any reference types should also be marked final so the user cant create unsafe mutating children.

You can also use actor and globalActor to make something Sendable.