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Junior — Middle

Can you explain the differences between launch and async functions when using Coroutine Builder in Kotlin?

sobes.tech AI

Answer from AI

In Kotlin, when working with coroutines, launch and async are Coroutine Builders, but they serve different purposes:

  • launch starts a coroutine that runs asynchronously and does not return a result. It is used for executing tasks where the result is not needed, such as side effects.

  • async starts a coroutine that returns a Deferred<T> — a deferred result that can be obtained using await(). It is used when you need to get the result of an asynchronous operation.

Example:

val job = scope.launch {
    // runs asynchronously, no result returned
}

val deferred = scope.async {
    // runs asynchronously, returns a result
    return@async 42
}

runBlocking {
    val result = deferred.await() // get the result
    println(result) // 42
}

In summary, launch is for starting tasks without a result, async is for starting tasks with a result.