This is not a valid type definition:
scala> type Addable = { def +(subject: Addable) }
<console>:4: error: illegal cyclic reference involving type Addable
type Addable = { def +(subject: Addable) }
Can this be expressed in scala?
views:
223answers:
3It does not work with the current nightly build.Welcome to Scala version 2.8.0.r18457-b20090810020144 (Java HotSpot(TM) Client VM, Java 1.6.0_12).Type in expressions to have them evaluated.Type :help for more information.scala> class A{ | type Addable = { def +(subject: Addable) } | }<console>:5: error: illegal cyclic reference involving method + type Addable = { def +(subject: Addable) }At least the error message changed :-).
Thomas Jung
2009-08-10 07:52:02
Did you try the experimental command line option mentioned at the bottom of the above article?
skaffman
2009-08-10 08:42:28
Same result with: scala -Yrecursion 10
Thomas Jung
2009-08-10 09:08:23
+1
A:
Here's what I did in a library I wrote, HTH:
trait Addable {
type AddableType <: Addable
def + (subject: AddableType): AddableType
}
trait Rational extends Addable {
type AddableType = Rational
override def + (subject: Rational): Rational
}
Yardena
2009-08-10 22:27:56
The definition has to be a structural type as the underlining classes cannot be changed (like Int, Long).
Thomas Jung
2009-08-12 05:11:00
Hm, perhaps you could define a view (implicit def) to convert these classes to Addable?
Yardena
2009-08-12 15:41:38