Working with Some() and Option() in Scala

Question

I've been fighting with the concept of the functional way of parsing a JSON string in Scala and ran flat into the wall with Option(something) being returned. I popped the questionand the helpful answers came streaming in.

The problem is, as someone being pretty new to Scala, what is the correct way?

Currently I'm doing this:

import util.parsing.json.JSON._

object JsonSoap {
  def main(args: Array[String]) {
    val x = parseFull("""{"name":"Joe","surname":"SOAP"}""")

    val y = x collect {
      case m: Map[_, _] => m collect {
        case (key: String, value: String) => key -> value
      }
    }

    val z = for (m <- y; name <- m.get("name"); surname <- m.get("surname"))
    yield {
      <soap:Envelope xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/">
        <soap:Body>
          <Person>
            <Name>{name}</Name>
            <Surname>{surname}</Surname>
          </Person>
        </soap:Body>
      </soap:Envelope>
    }

    println(z)
  }
}

I'm still stuck with Some()

Is there a nice pattern to solving my problem? Surely this has to be well explored territory. How can I improve my code?

Answer 1

You are not "stuck" with Some - you have the advantage that you have a Some! In Java, you would be stuck with a value whose type did not express the fact that it might not actually exist!

MyThing recklessly = apiCall.getMeAThing();
recklessly.iSureHopeImNotNull();  //OH NOES!

Compare that to this

apiCall.getMeAThing foreach (_.cannotPossiblyBeNull)

The Option datatype means that the "might not exist" bit of your query is actually baked into the return type of the query. Please stick with Option - in a few weeks you will be pulling out your hair when you go to write Java code and it's not there!

Shooting down your objections

You might say:

Aw, but I need to take the value I have and add 1 to it

I say:

apiCall.getMeAThing map (_ + 1)

You might say

Aw, but I need to pass it to a method, defaulting to the empty String if I have null

I say:

foo( apiCall.getMeAThing getOrElse "" )

You might say

Aw, but I use that value to call another API method and get something else

I say:

apiCall.getMeAThing flatMap apiCall.getMeAnotherThing

You'll definitely say

Aw but that's awfully inefficient with all those object creations

I say: "try it, it will be just fine"