Using the async/await syntax

The async/await syntax is the backbone of this structured concurrency. Let’s begin by understanding the async keyword.

async in Swift means that a function will perform some asynchronous operation, suspending the thread till the operation completes, and returning only when that operation is complete. Unlike a standard function, a function marked with the async keyword doesn’t block the caller but, rather, allows it to continue executing other tasks.

This is useful to perform IO-bound tasks, computationally intensive calculations, networking calls, and file operations, as it won’t stop the CPU while waiting – for instance, while waiting for data from a network operation.

An example of a Swift async function, illustrating the async syntax, is the following example code fragment:

// an example async function
import Foundation
func fetchData() async -> Data {
    // perform a network call
 ...