Question

Apparently Range has a method that checks if it contains a value of type Any. I understand that it is from SeqLike, but causes some problems.

For instance, i was matching hours from joda.DateTime:

DateTime.now match {
    case d if 0 to 12 contains d.hourOfDay() => ...

Here d.hourOfDay() returns DateTime.Property, not Int, but code still compiles, because of contains(elem: Any). Is there any way to check for such calls at compile time?

Answer 1

You can pimp Range to add a type-safer contains method:

class SafeRange( range: Range ) {
  def safeContains( i: Int ) = range contains i
}

object SafeRange {
  implicit def safer( range: Range ) = new SafeRange( range )
}

Import the implicit and call safeContains on any range instance:

scala> import SafeRange._
import SafeRange._

scala> (0 until 10) safeContains 3
res2: Boolean = true

scala> (0 until 10) safeContains 100
res3: Boolean = false

scala> (0 until 10) safeContains "foo"
<console>:18: error: type mismatch;
 found   : java.lang.String("foo")
 required: Int
          (0 until 10) safeContains