microdux.kt

fun <T : Any> MutableLiveData<T>.update(transform: (T) -> T) {
    val current = value ?: return
    postValue(transform(current))
}

class TinyViewModel() {
    private val initialState = UiState(greeting = "nah mate")
    private val _uiState = MutableLiveData(initialState)
    val uiState = _uiState as LiveData<String>
  
    fun sayYes() = _uiState.update {
        it.copy(greeting = "YES MATE!")
    }
}

data class UiState(
    val greeting: String
)