[WIP] Add methods to abstract over structure of case classes

[felixmulder]

Inspired by #1341, I decided to take a crack at improving case classes. These commits add two members to case classes:

• def fields: List[String]
• def toMap: Map[String, Any]

I think it is important to have a good way of abstracting over the members of case classes, this provides just that. One drawback to having this signature in the toMap method is that we loose type information. Ideally something like an HMap could be used here to retain type information.

There's room for improvement in this implementation as well - for instance def fields could of course be a @static val fields in the companion instead.

These two functions could in turn be used to improve the toString capabilities of case classes as well as various forms of pickling. Let me know your thoughts on this - if it feels like a step in the right direction, I wouldn't mind spending some time on this.

[odersky]

I see lots of ideas for improvements to case classes. Instead of trying to do this piece-wise I would prefer to have a very comprehensive SIP detailing how case classes should in the future support generic programming. I'll open an issue for this to serve as a place where discussions can take place.

[felixmulder]

Sounds good :)

[aisven]

@odersky or someone else: Please provide the link to the new issue where this is/was being discussed further.

[Blaisorblade]

@sourcekick I can't read Martin's mind, but the next issue, #1347, appears highly relevant.