Kotlin Programming: The Big Nerd Ranch Guide, 2nd Edition

async and await

async is a coroutine builder that can be used as an alternative to launch. Much like launch, async accepts a lambda expression as an argument, which is where you can call other code that suspends. The big difference between these two functions is their return types: launch returns a Job, but async returns an instance of Deferred.

These two classes are similar – in fact, Deferred extends from Job. But in addition to including information about the status of the coroutine, Deferred will also get a hold of the value returned by the coroutine. A Deferred value represents a value that might not be ready at this moment, but will be available eventually. The Deferred that is returned by async will receive whatever value ...