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I was going to call this “Grand Central Dispatch” but then I remembered this is supposed to be digestible chunks of information about Swift, not huge diatribes about the state of such-and-such tool. So, let’s continue with the simple task we have set out for us: moving to and from the background thread.

We’ve stumbled upon an easy one here as the syntax is not significantly different than in Objective-C. First, the version we are accustomed to:

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
	// do some task
	dispatch_async(dispatch_get_main_queue(), ^{
		// update some UI
	});
});

The only notable difference is that Swift code can use trailing closures, removing the need to remember to close the function parentheses later on:

let priority = DISPATCH_QUEUE_PRIORITY_DEFAULT
dispatch_async(dispatch_get_global_queue(priority, 0)) {
	// do some task
	dispatch_async(dispatch_get_main_queue()) {
		// update some UI
	}
}

Though if you’re using Swift and doing a lot of work in the background and taking action on main when that’s done, you may want to consider this clever operator by Josh Smith:

{ /* do some task */ } ~> { /* update some UI */}

Yes, you do have to include this other bit of code to use this operator but it really speaks to the power of implementing operators that do neat, compact things in Swift. Would I use it in code that someone else has to maintain? Maybe not.