Relation between scala Ordering and Scalaz Equals and Order

[Edmondo Porcu]

Dear all,

I am confused about these three typeclasses.

Which one should I prefer between Order and Ordering? Is there an implicit conversion from one to the other, and if it is the case, where is it found?

Best Regards

Edmondo

[Tom Switzer]

Ordering is an ADT that consists of 3 cases: LT, GT, and EQ. Order is a type class that defines an Order for some type. Scalaz's Order#compare returns an Ordering. You typically use both.

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[Edmondo Porcu]

What about implicit conversion? Which one do you implement?

2013/5/21 Tom Switzer <thomas....@gmail.com>

[Tom Switzer]

You implement scalaz.Order[A]. scalaz.Ordering is a sealed trait with 3 case objects as sub-types. You cannot implement it. It looks something like:

sealed trait Ordering

object Ordering {

  case object LT extends Ordering

  case object GT extends Ordering

  case object EQ extends Ordering

}

Instead of returning an Int from Order#compare, scalaz returns a scalaz.Ordering.

[Edmondo Porcu]

And when I want to do a sort on a collection, what should I import? Thank you for the precious indications

2013/5/21 Tom Switzer <thomas....@gmail.com>

[Tom Switzer]

Scalaz's Order has a method toScalaOrdering that returns a scala.math.Ordering instance. You can put this in scope as an implicit:

implicit val o = Order[A].toScalaOrdering

and then use Scala's collection's ordering methods.