Scala view bounds that work with subtypes?

Question

Is there anything in Scala like a view bound but which can match subtypes?

Since views in Scala do not chain, I currently have the following:

implicit def pimpIterable[A, I[_]](x: I[A])(implicit f: I[A] => Iterable[A]) =
  new { def mylength = x.size }

to let me write:

Array(1,2,3).mylength
Seq(1,2,3).mylength

The above form seems necessary since if I try to simplify my function signature with something like:

implicit def pimpIterable[A, I <% Iterable[A]](x: I) =
  new { def mylength = x.size }

then the implicit conversion won't work for Arrays since there is no direct view from Array to Iterable (only to a subclass of Iterable, which the first form is able to find).

This also forces all other short-hands to be written out in long form as well. What could have been:

implicit def pimpIterable[A: Scalar, I <% Iterable[A]](x: I) = ...

must now be written as:

implicit def pimpIterable[A, I[_]](x: I[A])(implicit f: I[A] => Iterable[A], m: Scalar[A]) = ...

Is there a Better Way?

Answer 1

There are two problems with the view bound signature. First, Iterable doesn't have length , only size . Next, I is not a type cosntructor. So, fixing both, the signature is:

implicit def pimpIterable[A, I <% Iterable[A]](x: I) = new { def mylength = x.size }

This is proper. If you parameterize I , it will exclude types such as BitSet and String .