Enriching NodeT about scala-graph HOT 6 CLOSED

You're right, the template TExtByImplicit.scala doesn't work correctly in your case. Armed with Scala 2.10, please try instead something like

final class ExtGraphNode[N, E[X] <: EdgeLikeIn[X]](g: Graph[N,E])(node: g.NodeT) {
  def inHead = node.inNeighbors.head
}
val g = Graph(1 ~> 2, 2 ~> 3)
implicit def toExt(node: g.NodeT) = new ExtGraphNode(g)(node)
(g get 1).inHead.shortestPathTo(g get 3)

Looking forward to your feedback
Peter

from scala-graph.

Thanks for the fast response. I tried your code and it works as it is but If we rename the graph parameter the way shown below, the code will not compile asking for the value g2:

final class ExtGraphNode[N, E[X] <: EdgeLikeIn[X]](g2: Graph[N,E])(node: g2.NodeT) {
  def inHead = node.inNeighbors.head
}
val g = Graph(1 ~> 2, 2 ~> 3)
implicit def toExt(node: g.NodeT) = new ExtGraphNode(g)(node)
(g get 1).inHead.shortestPathTo(g get 3)

That is, g in g.NodeT is coming from the instance of the graph object rather from the first parameter list which makes it impossible to implement enrich my library pattern. Perhaps it has something to do with the general idea of enriching the inner class.

from scala-graph.

After giving some thought to the issue I suspect that for the original code to work the compiler needs to be able to infer that the containingGraph instance of the node_ parameter is the same as the instance g which is impossible at the compile time. A simple but not very elegant workaround is to cast the returned node.

(g get 1).inHead.asInstanceOf[g.NodeT].shortestPathTo(g get 3)

Let me know if you have any other ideas.

from scala-graph.

Gleb,
Thanks for investigating.Casting does help but I'm not satisfied with it,
either. Clearly, we must find out the 'right way'. I'll look into it in the
following days. You may use asInstanceOf as a workaround so long.

2013/6/6 Gleb Sizov [email protected]

After giving some thought to the issue I suspect that for the original
code to work the compiler needs to be able to infer that the
containingGraph instance of the node_ parameter is the same as the instance
g which is impossible at the compile time. A simple but not very elegant
workaround is to cast the returned node.

(g get 1).inHead.asInstanceOf[g.NodeT].shortestPathTo(g get 3)

Let me know if you have any other ideas.

—
Reply to this email directly or view it on GitHubhttps://github.com//issues/4#issuecomment-19028924
.

from scala-graph.

Hi Gleb,
you may find two further node enrichment alternatives at [https://github.com/scala-graph/scala-graph/blob/master/core/src/test/scala/custom/TExtByImplicit.scala]. I'd strongly prefer the way outlined in 'test_nodeEnrichment_3' because it is fully type safe and requires less resources at run time than 'test_nodeEnrichment_2'. The only drawback is that you need to instantiate ExtGraph and import the implicit conversion for each graph instance.
Can you go with it?
Peter

from scala-graph.

Hi Peter,

I will go for 'test_nodeEnrichment_3' because of the reasons you outlined above. In general, type safe enrichment of inner classes in Scala seems to require the kind of boilerplate code you have in 'test_nodeEnrichment_3'. I posted a relevant question on stackoverflow: http://stackoverflow.com/questions/16977730/enrich-an-inner-class

Thanks for help,
Gleb

from scala-graph.