Kotlin Programming: The Big Nerd Ranch Guide, First Edition

launch vs async/await

The async and launch functions that you used to perform the request and update the UI are called coroutine builder functions, functions that set up a coroutine to perform work in a certain way. launch builds a coroutine that performs the work you specify right away – in this case, calling fetchCharacterData and updating the UI.

The async coroutine builder works differently than launch in that it builds a coroutine that returns a Deferred, a type that represents work that has not been completed yet. Instead of starting the work immediately, a Deferred is a promise of work to be completed some time in the future.

The Deferred type provides a function called await that you call when you would like the work to ...