arrow-fx-stm/arrow.fx.stm/STM/write

write

abstract fun <A> TVar<A>.write(a: A)

Set the value of a TVar.

import arrow.fx.stm.TVar
import arrow.fx.stm.atomically

suspend fun main() {
  //sampleStart
  val tvar = TVar.new(10)
  val result = atomically {
    tvar.write(20)
  }
  //sampleEnd
  println(result)
}

Similarly to read this comes with a few guarantees:

For multiple writes to the same TVar in a transaction only the last will actually be performed
When committing the value inside the TVar, at the time of calling write, has to be the same as the current value otherwise the transaction will retry

open fun <A> TQueue<A>.write(a: A)

Append an element to the TQueue.

import arrow.fx.stm.TQueue
import arrow.fx.stm.atomically

suspend fun main() {
  //sampleStart
  val tq = TQueue.new<Int>()
  atomically {
    tq.write(2)
  }
  //sampleEnd
  println("Items in queue ${atomically { tq.flush() }}")
}

This function never retries.