swift array construction looping through an async function [duplicate]

Question

G'day, I have to loop through an array of objects and perform an operation on each item where the result is returned asynchronously. I'm very new to async/await style of coding in Swift and could not figure out how to find an easier solution. Appreciate any help. Please find the sample code below. I tried surrounding it inside Task but it does not work due to compiler error.


func performOperation(ids: [UUID]) -> [TypeA] {

var output: [TypeA] = []

for id in ids { 
  Task {
    let results = await someAsyncFunction(id)
    output.append(contendsOf: results)  // Does not compile.
  }
}

return output

}

func someAsyncFunction(id: UUID) async -> [TypeA] {
 // third party framework function.
}

Ricky Mo · Accepted Answer · 2024-01-23 04:26:10Z

2

It is generally not recommended to wait for async task synchronously, so once there is an async callee in the call stack, you have to modify all the callers to become async, up until one that doesn't need to return a value depending on the async call.

func performOperation(ids: [UUID]) async -> [TypeA]  {  //make this async
    var output: [TypeA] = []
    for id in ids {
        let results = await someAsyncFunction(id)
        output.append(contentsOf: results)
    }
    return output
}

func main(){
    Task{
        let output = performOperation(ids: ids)
    }
}

answered Jan 23, 2024 at 4:26

Ricky Mo

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3 Comments

Alexander Over a year ago

This isn’t quite the same, because the items are all computed serially

Ricky Mo Over a year ago

Though OP doesn't mention whether serial or parallel is preferred. If parallel is preferred, check out taskGroup.waitForAll() in this post: stackoverflow.com/questions/76781545/…

Mev Over a year ago

Thank you both and the moderator that pointed me in the right direction towards TaskGroups. That's exactly what I have been looking for.

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