CODEWITHSUNDEEP
javascalaimplicit-conversion
jrook
jrook

Reputation: 3519

Optimal way to create implicit view for Java objects in Scala

I am working with a Java library. This library has a bunch of collections for which I want to have implicit views in my Scala code. The Java library's object model follows a pattern like this:

(NarrowStreet | WideStreet) extends Street extends Road extends TwoNode

StreetList extends java.util.AbstractList< Street>

RoadList extends java.util.AbstractList< Road>

and so on. A StreetList virtually behaves like a List<Street>.

I need to use a method in this library which has the following signature:

List<StreetList> city.getStreets();

In Scala, I do the following to implicitly get to a Seq[Street] collection:

implicit def twoNodeView[T <: java.util.AbstractList[_ <: TwoNode]](x : T): Seq[_ <: TwoNode] = for(i <- 0 until x.size()) yield x.get(i)

Now when I do

city.getStreets.asScala.flatten //.map, .filter, etc.

it gives me a Seq[TwoNode]. I cast the objects when I use the collection in a map or filter function and I think I am safe since I am 100% sure that this object is a Seq[Street] and not really a Seq[TwoNode].

Questions:

  1. Are there any fail scenarios the way I am implementing the implicit view?

  2. Can this be improved or is there a better way to achieve the same result and avoid casting?

Upvotes: 0

Views: 75

Answers (1)

Alexey Romanov
Alexey Romanov

Reputation: 170745

You don't need to define your own implicits for this. Just use

city.getStreets.asScala.map(_.asScala)

to get the nested Buffer[Buffer[Street]] and then .flatten it into Seq[Street] if you want.

Upvotes: 2

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