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

Answer 1

(Note: Swift 5 may support await as you’d expect it in ES6!)

What you want to look into is Swift's concept of "closures". These were previously known as "blocks" in Objective-C, or completion handlers.

Where the similarity in JavaScript and Swift come into play, is that both allow you to pass a "callback" function to another function, and have it execute when the long-running operation is complete. For example, this in Swift:

func longRunningOp(searchString: String, completion: (result: String) -> Void) {
    // call the completion handler/callback function
    completion(searchOp.result)
}
longRunningOp(searchString) {(result: String) in
    // do something with result
}        

would look like this in JavaScript:

var longRunningOp = function (searchString, callback) {
    // call the callback
    callback(err, result)
}
longRunningOp(searchString, function(err, result) {
    // Do something with the result
})

There's also a few libraries out there, notably a new one by Google that translates closures into promises: https://github.com/google/promises. These might give you a little closer parity with await and async.