Challenge 2: A StateFlow Counter — Solution

import kotlinx.coroutines.*
import kotlinx.coroutines.flow.*

fun main() = runBlocking {
    val counter = MutableStateFlow(0)

    val collectorJob = launch {
        counter.collect { value ->
            println("Counter is now: $value")
        }
    }

    delay(100)
    counter.value = 1
    delay(100)
    counter.value = 2
    delay(100)
    counter.value = 3
    delay(100)

    collectorJob.cancel()
}

/*
Output:
Counter is now: 0
Counter is now: 1
Counter is now: 2
Counter is now: 3

Notes:
- The collector immediately receives the initial value (0) as soon as it
  starts collecting, since StateFlow always holds a current value.
- Each counter.value = ... assignment is picked up by the collecting
  coroutine and printed, since StateFlow is hot and broadcasts updates
  to every active collector.
- collectorJob.cancel() stops the collecting coroutine at the end so
  runBlocking can finish — without cancelling it, the collect { } call
  would keep suspending forever waiting for more updates, and the
  program would never exit.
*/