Correct way to expose MutableLiveData as LiveData?

From the Java perspective, Method A has one less field in the class, thus is "more" efficient. From the Kotlin perspective, Method B denotes a bit more clearly, that the non-mutable property is a direct reference to the mutable one. Also Kotlin is clever enough to locally access the field rather than the getter method.

Is there a reason to use Method B over Method A?

In general is merely a matter of taste. Looking at it from a micro-optimization perspective it depends on whether or not you'd also use this reference within the class itself.

Starting from Kotlin 1.4-M2 you can do simply:

private val myMutableLiveData = MutableLiveData<String>()
val myLiveData : LiveData<String> by this::myMutableLiveData

The this:: is unfortunately needed, otherwise does not compile.

I found this in Igor Wojda's answer which discusses other approaches. Unfortunately his answer in this question was deleted.