Scala Cookbook

20.6. Using the Option/Some/None Pattern

Problem

For a variety of reasons, including removing null values from your code, you want to use what I call the Option/Some/None pattern. Or, if you’re interested in a problem (exception) that occurred while processing code, you may want to return Try/Success/Failure from a method instead of Option/Some/None.

Solution

There is some overlap between this recipe and the previous recipe, “Eliminate null Values from Your Code”. That recipe shows how to use Option instead of null in the following situations:

• Using Option in method and constructor parameters

• Using Option to initialize class fields (instead of using null)

• Converting null results from other code (such as Java code) into an Option

See that recipe for examples of how to use an Option in those situations.

This recipe adds these additional solutions:

• Returning an Option from a method

• Getting the value from an Option

• Using Option with collections

• Using Option with frameworks

• Using Try/Success/Failure when you need the error message (Scala 2.10 and newer)

• Using Either/Left/Right when you need the error message (pre-Scala 2.10)

Returning an Option from a method

The toInt method used in this book shows how to return an Option from a method. It takes a String as input and returns a Some[Int] if the String is successfully converted to an Int, otherwise it returns a None:

def toInt(s: String): Option[Int] = {
  try {
    Some(Integer.parseInt(s.trim))
  } catch {
    case e: Exception => None
  }
}

Although this is a simple ...