A helper class that exposes observables for two different types, as well as a single observable for both

RelayPair.kt

class RelayPair<A, B> {
  private val relayA = BehaviorRelay.create(null as A?)
  private val relayB = BehaviorRelay.create(null as B?)
  private val relayBoth = BehaviorRelay.create(Both<A, B>(null, null))

  data class Both<out A, out B>(val a: A?, val b: B?)

  fun publishA(value: A?) {
    relayA.call(value)
    relayBoth.call(relayBoth.value.copy(a = value))
  }

  fun publishB(value: B?) {
    relayB.call(value)
    relayBoth.call(relayBoth.value.copy(b = value))
  }

  fun publishBoth(a: A?, b: B?) {
    relayA.call(a)
    relayB.call(b)
    relayBoth.call(Both(a, b))
  }

  fun observeA(): Observable<A?> = relayA

  fun getA(): A? = relayA.value

  fun observeB(): Observable<B?> = relayB

  fun getB(): B? = relayB.value

  fun observeBoth(): Observable<Both<A, B>> = relayBoth
}