Option. A function computes a return value. But sometimes nothing valid can be returned. Nothing is possible. With an Option, we can specify None instead of a value.
With optional data, our algorithms become clearer. We clearly specify whether "None" or something valid is available. We indicate absence.
Return Option example. Here the getName def returns an Option String. If the argument we pass to it is at least 1, we get an Option containing the String "Oxford."
However If the value is 0 or less, we get None, which is an option with no value.
def getName(value: Int): Option[String] = {
// Return a String Option based on the argument Int.
if (value >= 1) {
return Option("Oxford")
}
else {
return None
}
}
object Program {
def main(args: Array[String]): Unit = {
// Accepted to Oxford.
println(getName(10))
// Rejected.
println(getName(0))
}
}Some(Oxford)
None
Option, Map. The Map collection uses an Option when we call its get() method. Sometimes nothing exists at the key specified. None is returned.
Note With an Option, we can always call isDefined. This returns true if the Option does not have a None value, and false otherwise.
Return An option will return its inner value (in this case, a String) when the get() method is invoked.
object Program {
def main(args: Array[String]): Unit = {
val ids = Map(("a12", "Mark"), ("b19", "Michelle"))
// Get Option from our map.
val result = ids.get("b19")
if (result.isDefined) {
println(result.get)
}
}
}Michelle
GetOrElse. Here is another method on an Option. We can use getOrElse to access the inner value of the Option, unless there is None. If None, we get the argument back.
So We provide a default value. This helps us handle cases where None can occur.
object Program {
def main(args: Array[String]): Unit = {
val words = Map(1000 -> "one-thousand", 20 -> "twenty")
// This returns None as the Option has no value.
val result = words.get(2000)
println(result)
// Use getOrElse to get a value in place of none.
val result2 = result.getOrElse("unknown")
println(result2)
}
}None
unknown
Null, None. We can use the null keyword in assignments. But for top-quality code, Option is preferred. Generally in languages we like to copy the core types like Map, which uses Options.
List find. The find() method on Lists returns an Option. It may be clearer to use find() instead of indexOf() as we can test the option to determine if an element was not found.
Many things in life are optional. For these things, we can use an Option type in Scala. With an Option, we express absence or "nothingness" with clarity.
Dot Net Perls is a collection of tested code examples. Pages are continually updated to stay current, with code correctness a top priority.
Sam Allen is passionate about computer languages. In the past, his work has been recommended by Apple and Microsoft and he has studied computers at a selective university in the United States.
This page was last updated on Dec 15, 2023 (edit).