zip.kt

fun <T1, T2, R> zip(
    source1 : LiveData<T1?>,
    source2 : LiveData<T2?>,
    source1Name: String = "first",
    source2Name: String = "second",
    zipFunction: (t1:T1?, t2:T2?, emitter:(R)->Unit) -> Unit
): LiveData<R>{
    return object : MediatorLiveData<R>(){
        var t1: T1? = null
        var t2: T2? = null
        var emit:(r: R)-> Unit = { r ->
            value = r
        }
        init {
            addSource(source1){
                Timber.d("zip by $source1Name:$it")
                t1 = it
                zipFunction(t1, t2, emit)
            }
            addSource(source2){
                Timber.d("zip by $source2Name:$it")
                t2 = it
                zipFunction(t1, t2, emit)
            }
        }
    }
}