Getting Comparison Functions in Scala

Question

I am playing around with sorting algorithms. I was curious if there were built-in comparison functions for the primitive types. I know it is really easy just to type (x: Int, y: Int) => x - y. I just want to know if there is a built in comparison, so I'm not reinventing the wheel. Things obviously get more complicated when it comes to Strings (case-sensitive and culture sensitive). I would be surprised if there wasn't something already built-in.

_ - _ is even easier, or, if type inference is not available, (_: Int) - (_: Int). — Erik Kaplun
– Erik Kaplun, Commented Jul 31, 2014 at 14:34

Travis Brown · Accepted Answer · 2014-07-30 13:48:41Z

5

If a type A has an Ordering instance, you can get it by writing Ordering[A], and Ordering has a compare method that you can eta-expand to the function you're looking for:

scala> Ordering[Int].compare _
res0: (Int, Int) => Int = <function2>

As a special case for the primitives (and a few other types), you can refer to the instance directly:

scala> Ordering.Int.compare _
res1: (Int, Int) => Int = <function2>

And more generally, if you've got a type class F and A has an instance, you can get that instance by writing implicitly[F[A]], so the following also works:

scala> implicitly[Ordering[Int]].compare _
res2: (Int, Int) => Int = <function2>

I'd use the first of these choices, though.

answered Jul 30, 2014 at 13:48

Travis Brown

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