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scalaimplicitscala-option

Scala: How can I explicitly compare two Options?

If I have two Options such as 

val a = Option(2)
val b = Option(1)

I can write

List(a,b).sorted

and it sorts correctly by inserting an implicit Ordering. How can I get a reference to this Ordering so I can call compare(a,b) and get the result? I'd like the equivalent of

val comparison = a.compare(b)

except without having a and b be instances of Ordered.

Solution

  • You can just ask for the ordering implicit directly:

    Welcome to Scala version 2.10.3 (Java HotSpot(TM) 64-Bit Server VM, Java 1.7.0_21).
Type in expressions to have them evaluated.
Type :help for more information.

scala> implicitly[Ordering[Option[Int]]]
res0: Ordering[Option[Int]] = scala.math.Ordering$$anon$3@501a9177

scala> res0.compare(Some(1), Some(3))
res1: Int = -1