How to make async / await in Swift?

Question

I would like to simulate async and await request from Javascript to Swift 4. I searched a lot on how to do it, and I thought I found the answer with DispatchQueue, but I don't understand how it works.

I want to do a simple stuff:

if let items = result.value {     var availableBornes = [MGLPointFeature]()      for item in items {         guard let id = item.id else { continue }          let coordinate = CLLocationCoordinate2D(latitude: Double(coor.x), longitude: Double(coor.y))          // ...          // This is an asynchronous request I want to wait         await _ = directions.calculate(options) { (waypoints, routes, error) in             guard error == nil else {                 print("Error calculating directions: \(error!)")                 return             }              // ...              if let route = routes?.first {                 let distanceFormatter = LengthFormatter()                 let formattedDistance = distanceFormatter.string(fromMeters: route.distance)                 item.distance = formattedDistance                  // Save feature                 let feature = MGLPointFeature()                  feature.attributes = [                     "id": id,                     "distance": formattedDistance                 ]                  availableBornes.append(feature)              }         }     }      // This should be called after waiting for the async requests     self.addItemsToMap(availableBornes: availableBornes) } 

What should I do?

Answer 1

Thanks to vadian's comment, I found what I expected, and it's pretty easy. I use DispatchGroup(), group.enter(), group.leave() and group.notify(queue: .main){}.

func myFunction() {     let array = [Object]()     let group = DispatchGroup() // initialize      array.forEach { obj in          // Here is an example of an asynchronous request which use a callback         group.enter() // wait         LogoRequest.init().downloadImage(url: obj.url) { (data) in             if (data) {                 group.leave() // continue the loop             }         }     }      group.notify(queue: .main) {         // do something here when loop finished     } }