Swift now supports asynchronous (async) functions, enabling us to run complicated asynchronous code almost as if it were synchronous thanks to SE-0296. As in other languages like C# and JavaScript, this is accomplished in two steps: first, async functions are identified using the new &#x5C;&#96;&#96;async&#96;&#x5C;&#96; keyword, and then they are called with the &#96;await&#96; keyword. Let’s take a look at a few code examples to understand exactly how to use **await** and **async** in Swift.

&#x5C;
 ![](https:&#x2F;&#x2F;firebasestorage.googleapis.com&#x2F;v0&#x2F;b&#x2F;dopebase-9b89b.appspot.com&#x2F;o&#x2F;async-await-swift.png?alt=media&amp;token=ea112f4e-bc86-4092-9b71-b78167916da2)

&#x5C;
Let’s start with a quick example so you can see what the syntax for **async** and **await** looks like in **Swift** - most of the code should be self-explanatory.

## Async Await in Swift - Example

&#96;&#96;&#96;javascript
func fetchSomethingFromServer() async -&gt; [Double] {
    &#x2F;&#x2F; This can be a network request, a file data read, anything expensive really.
    (1...10000).map { _ in Double.random(in: -10...30) }
}

func average(for results: [Double]) async -&gt; Double {
    let sum = results.reduce(0, +)
    let avg = sum &#x2F; Double(results.count)
    return avg
}

func upload(result: Double) async -&gt; String {
    &#x2F;&#x2F; upload something to a server, this can be any expensive operation
    return &quot;Done&quot;
}
&#96;&#96;&#96;

&#x5C;
We’ve implemented 3 different **async** functions - notice the &#96;async&#96; keyword in their signature - this means that the blocks are dispatched to a background queue, and are run asynchronously.

Let’s see now how we can call these methods in order to actually process the results, and not just obtain a reference to the execution promise.

&#96;&#96;&#96;javascript
func processEverything() async {
    let results = await fetchSomethingFromServer()
    let avg = await average(for: results)
    let response = await upload(result: avg)
    print(&quot;Server response: &#x5C;(response)&quot;)
}
&#96;&#96;&#96;

&#x5C;
As you can see, all of the indenting and closures have been removed, leaving what is frequently referred to as &quot;straight-line code&quot;; except from the await keywords, it resembles synchronous code. Because the execution is linear, it is simple to understand and reason about. While we&#x27;re still doing occasionally difficult asynchronous jobs, it will be simpler to understand asynchronous programming, as using **await** &#x2F; **async** in Swift is clearly a lot more readable.

&#x5C;
There are a few simple, clear guidelines that govern how async functions operate:

* Swift will generate an error if synchronized functions attempt to invoke async functions directly because that wouldn&#x27;t make sense.
* Async functions have the ability to call other async functions, but they can also, if necessary, call synchronous functions.
* Swift will favor the function that best fits the current context if you have async and synchronous functions that can be called in the same way. If the call site is now async, Swift will call the async function; if not, it will call the synchronous function.

## Calling Await from Synchronous Functions

You cannot use await in a synchronous environment. To be able to leverage async &#x2F; await from a synchronous method, you can use &#96;Task.init&#96; like in the example below:

&#96;&#96;&#96;javascript
func fetchSomeData() {
        Task.init {
            do {
                self.results = try await fetchResults()
            } catch {
                &#x2F;&#x2F; .. handle error
            }
        }
    }
&#96;&#96;&#96;

## Async &#x2F; Await with Try &#x2F; Catch

**Async functions** and initializers now have the ability to throw errors when necessary thanks to the advent of &#96;async&#96;&#x2F;&#96;await&#96;, which perfectly complements &#96;try&#96;&#x2F;&#96;catch&#96;. The one exception is that Swift mandates a specific order for the keywords, and between call site and function, that order is inverted.

&#x5C;
Here’s a code example of how to use async await in Swift within a try - catch block:

&#96;&#96;&#96;javascript
do {
    let data = try await fetchData()
    let processedData = try await process(data)
    print(&quot;Fetched &#x5C;(processedData.count) results.&quot;)
} catch {
    print(&quot;Fetching data failed with error &#x5C;(error)&quot;)
}
&#96;&#96;&#96;

&#x5C;
This is pretty much everything you need to know about async await in Swift. If you think there’s anything we missed, please let us know.  Additionally, if you found this tutorial helpful, please share it on Twitter, to help us spread the word. Thanks!

Async Await in Swift with Code Examples | Devbrite

&lt;ul class=&quot;table-of-contents&quot;&gt;
  &lt;li&gt;
    &lt;a href=&quot;#async-await-in-swift---example&quot;&gt;Async Await in Swift&lt;&#x2F;a&gt;
  &lt;&#x2F;li&gt;
  &lt;li&gt;
    &lt;a href=&quot;#calling-await-from-synchronous-functions&quot;&gt;Calling Await from Synchronous Functions&lt;&#x2F;a&gt;
  &lt;&#x2F;li&gt;
  &lt;li&gt;
    &lt;a href=&quot;#async---await-with-try---catch&quot;&gt;Async &#x2F; Await with Try &#x2F; Catch&lt;&#x2F;a&gt;
  &lt;&#x2F;li&gt;
&lt;&#x2F;ul&gt;

Async Await in Swift with Code Examples

About

Legal

Products

Resources