In #183, I talked about Quality of Service (QoS) classes that were introduced in iOS 8. Async is a small library providing syntax sugar for GCD, supporting QoS.

Instead of doing this the pre-QoS classes way:

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0), {
    print("This runs on the background queue")

    dispatch_async(dispatch_get_main_queue(), {
        print("This runs on the main queue, after the previous block")
    })
})

You can do:

Async.background {
    print("This runs on the background queue")
}.main {
    print("This runs on the main queue, after the previous block")
}

There's a couple of examples in the README, including chaining blocks so you don't end up with many levels of code indentation. Check it out.

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