//arrow-fx-coroutines/arrow.fx.coroutines/Resource/parZip

parZip

common fun <B, C> parZip(fb: Resource<B>, f: suspend (A, B) -> C): Resource<C>

common fun <B, C> parZip(ctx: CoroutineContext = Dispatchers.Default, fb: Resource<B>, f: suspend (A, B) -> C): Resource<C>

Composes two Resources together by zipping them in parallel, by running both their acquire handlers in parallel, and both release handlers in parallel.

Useful in the case that starting a resource takes considerable computing resources or time.

import arrow.fx.coroutines.*
import kotlinx.coroutines.delay

class UserProcessor {
  suspend fun start(): Unit { delay(750); println("Creating UserProcessor") }
  fun shutdown(): Unit = println("Shutting down UserProcessor")
  fun process(ds: DataSource): List<String> =
   ds.users().map { "Processed $it" }
}

class DataSource {
  suspend fun connect(): Unit { delay(1000); println("Connecting dataSource") }
  fun users(): List<String> = listOf("User-1", "User-2", "User-3")
  fun close(): Unit = println("Closed dataSource")
}

class Service(val db: DataSource, val userProcessor: UserProcessor) {
  suspend fun processData(): List<String> = userProcessor.process(db)
}

//sampleStart
val userProcessor = resource {
  UserProcessor().also { it.start() }
} release UserProcessor::shutdown

val dataSource = resource {
  DataSource().also { it.connect() }
} release DataSource::close

suspend fun main(): Unit {
  userProcessor.parZip(dataSource) { userProcessor, ds ->
      Service(ds, userProcessor)
    }.use { service -> service.processData() }
}
//sampleEnd

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