Simple wrapper over MediatorLiveData to build relations between LiveDatas in Android ViewModels

DependantLiveData.kt

inline fun <T> dependantLiveData(vararg dependencies: LiveData<*>, crossinline mapper: () -> T?) =
    MediatorLiveData<T>().also { mediatorLiveData ->
        val observer = Observer<Any> { mediatorLiveData.value = mapper() }
        dependencies.forEach { dependencyLiveData ->
            mediatorLiveData.addSource(dependencyLiveData, observer)
        }
    }

//Example usage

class UserViewModel(private val resourceProvider: ResourceProvider) : ViewModel() {

    val firstName = MutableLiveData<String>()
    val lastName = MutableLiveData<String>()

    val displayName = dependantLiveData(firstName, lastName) {
        resourceProvider.getString(R.string.display_name, firstName.value.orEmpty(), lastName.value.orEmpty())
    }
}