Comments on: Fun with C# generics: down-casting to a generic type

By: Andrew Borodin

Andrew Borodin — Sun, 30 May 2010 12:09:14 +0000

Usefulll casting, btw. Thx (:

By: Andrew Borodin

Andrew Borodin — Sun, 30 May 2010 12:05:28 +0000

Small typo
public override Pair ConstructPair(Node secondNode) {
return other.ConstructPair(this);
}

By: MASHA

MASHA — Mon, 19 Apr 2010 18:57:47 +0000

Ok i see…but it wasnt tags ) last one

i just ment that when return new Pair i am to use type not TFirst, but (i’ve just called it not to have Classes with the same names, so i have not Node and Node’T’ but Node and TypedNode’T')
TypedNode’TFirst’ and TypedNode’T’ instead of just ‘T’.

ps why skipping text in angular brackets…

By: MASHA

MASHA — Mon, 19 Apr 2010 18:45:02 +0000

Hmmmm…
Why did browser skipped my post in thi strange way ?
Ok, i just ment that when return new Pair i am to use type not TFirst, but (i’ve just called it not to have Classes with the same names, so i have not Node and Node but Node and TypedNode)
TypedNode and TypedNode instead of just .
Thats all)
ps Fix this browser’s strange behavior!)

By: MASHA

MASHA — Mon, 19 Apr 2010 18:33:38 +0000

Hi there!
Good idea. But …I still had compilation error untill changed this:
return new Pair(firstNode, this);
Anyway, I solved my problem, so thanks!

By: Wigy

Wigy — Mon, 15 Feb 2010 21:36:57 +0000

I am just catching up with your blog, Igor. Congrats, you have great content. The problem you described here is quite interesting. Having a heterogeneous collection like your linked list and depending on the type of 2 elements is not trivial. Knowing you have a single algorithm (building pairs) and that you have only a single generic class that implements the Node interface, it is quite elegant to just ask the abstract Node class for some help. This way you could avoid implementing a 3-way dispatch by generalizing the visitor pattern.

By: Igor Ostrovsky

Igor Ostrovsky — Wed, 09 Sep 2009 19:28:59 +0000

You can get on the data in solution #3… that’s actually the point. The trick is to add a virtual method DoSomething on the non-generic Node class, and then override it in the Node generic class. In DoSomething in the derived generic class, you can access T (the data) in a type-safe way.

My approach #3 requires that you are able to add a method to the Node class. If you can’t do that, use approach #2. See my explanation to orastem for some details on how to do that.

By: Chad

Chad — Wed, 09 Sep 2009 19:18:19 +0000

Thanks. Follow-up: when operating on your tree of nodes, did you ever need to get to the Data? Seems like the only way to get at the Data would be your Solution #1.

Context of my question: If your nodes were stored in a DB, and you wanted to expose them to a consumer, as some kind of generic collection, the collection would have to be typed to the abstract class, and the consumer would have to down-cast the nodes in order to get to the Data. I think similar to your solution #1.

Do you have a solution for getting at the data more along the lines of your Solution #3?

By: Igor Ostrovsky

Igor Ostrovsky — Wed, 09 Sep 2009 19:01:20 +0000

Chad:

Yes, you could have a list of non-generic nodes. In the scenario I encountered, I actually had a tree of them.

By: Chad

Chad — Wed, 09 Sep 2009 18:50:22 +0000

Very nice. I am still trying to get a feel for generic classes, so excuse the ignorance.

Is one of the reasons for the abstract Node so that you can consume a generic list of nodes: List myModes;

And it would be on the consumer to check the type of of the individual concrete nodes in the list?