Circular dependency in Scala collections

Question

Trait Traversable has methods such as toList, toMap, ToSeq. Given that List, Map, Seq are subclasses of Traversable, this creates a circular dependency, which is generally not a desirable design pattern.

I understand that this is constrained to the collections library and it provides some nice transformation methods.

Was there any alternative design considered? Such as a "utility" class, or adding the conversion methods to Predef?

Say I want to add a new class: class RandomList extends List {...}. It would be nice to have a method toRandomList available for all Traversable classes, but for that I would need to "pimp my library" with an implicit on Traversable? This seems a bit of an overkill. With a utility class design, I could just extend that class (or Predef) to add my conversion method. What would be the recommended design here?

Answer 1

An alternative and extensible approach would be to[List], to[RandomList].

It's a bit tricky to add this with implicits, though. https://gist.github.com/445874/2a4b0bb0bde29485fec1ad1a5bbf968df80f2905