Question

Scalaz has an asMA method, but no asIdentity method. The following produces a compilation error in Scala 2.9.1 as shown:

Some(0).max(None)

<console>:14: error: type mismatch;
 found   : None.type (with underlying type object None)
 required: Ordering[?]
              Some(0).max(None)
                          ^

which can be fixed with an explicit cast:

(Some(0):Identity[Option[Int]]).max(None)

It seems to me that this would be more elegant, if asIdentity existed:

Some(0).asIdentity.max(None)

Answer 1

You can use the fact that Identity has a Pure instance:

scala> some(0).pure[Identity] max None
res0: Option[Int] = Some(0)

Note that you need to use some(0) instead of Some(0) here so that you start with something of type Option[Int] instead of Some[Int].

There’s also Identity.apply:

scala> Identity(some(0)) max None
res1: Option[Int] = Some(0)

Given these options—and the fact that explicitly indicating that you want to wrap something in Identity is only necessary in a handful of cases like this, where you need to disambiguate—I’d guess the Scalaz designers just didn’t see the need for an additional asIdentity method.