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I have started a project to write an async PostgreSQL driver on Scala and to be async, I need to accept callbacks and use futures, but then accepting a callback and a future makes the code cumbersome because you always have to send a callback even if it is useless.

Here's a test:

"insert a row in the database" in {

  withHandler {
    (handler, future) =>
      future.get(5, TimeUnit.SECONDS)
      handler.sendQuery( this.create ){ query =>  }.get( 5, TimeUnit.SECONDS )
      handler.sendQuery( this.insert ){ query =>  }.get( 5, TimeUnit.SECONDS ).rowsAffected === 1


Sending the empty callback is horrible but I couldn't find a way to make it optional or anything like that, so right now I don't have a lot of ideas on how this external API should look like.

It could be something like:

handler.sendQuery( this.create ).addListener { query => println(query) }

But then again, I'm not sure how people are organizing API's in this regard. Providing examples in other projects would also be great.

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No, you just use futures and don't call get on them unless absolutely necessary. Instead, you add callbacks to the futures and transform and compose futures with combinators. See Twitter Util futures and Akka futures.

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If you are talking async and futures in Scala, it is imperative that you read SIP-14: Futures and Promises. There were also some extensive discussions about it on the SIP mailing list, which is a google group, so you can find its archives.

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