`Task` at `createSampleData` function in What's new in SwiftData session

Question

Created Jun ’24

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Participants 3

I was looking to the example code that point from What's new in SwiftData session and noticed something that I cannot understand about Swift concurrency. from this snippet:

       static func createSampleData(into modelContext: ModelContext) {
        Task { @MainActor in
            let sampleDataTrips: [Trip] = Trip.previewTrips
            let sampleDataLA: [LivingAccommodation] = LivingAccommodation.preview
            let sampleDataBLT: [BucketListItem] = BucketListItem.previewBLTs
            let sampleData: [any PersistentModel] = sampleDataTrips + sampleDataLA + sampleDataBLT
            sampleData.forEach {
                modelContext.insert($0)
            }
            
            if let firstTrip = sampleDataTrips.first,
               let firstLivingAccommodation = sampleDataLA.first,
               let firstBucketListItem = sampleDataBLT.first {
                firstTrip.livingAccommodation = firstLivingAccommodation
                firstTrip.bucketList.append(firstBucketListItem)
            }
            if let lastTrip = sampleDataTrips.last,
               let lastBucketListItem = sampleDataBLT.last {
                lastTrip.bucketList.append(lastBucketListItem)
            }
            try? modelContext.save()
        }
    }

From the code snippet, I cannot see any task that needs to be marked with await, and it is also marked as @MainActor.

My question is: why do we need to put Task here? It seems like all the code will run on the main thread anyway. I am just afraid that I might be missing some concept of Swift concurrency or SwiftData here.

Thank you

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Answer 1

marchyman OP

Jun ’24

Task { @MainActor in ... } forces the code between the braces to run on the main actor. It also allows the code to run when the main actor is not otherwise busy doing something else. The code is not synchronous. createSampleData will create the task and immediately return.

0

Answer 2

enodev OP

Jun ’24

Yeah, but since the whole block will run/block the MainActor later, the question of OP I think is why is it done this way.

2