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Re: [cross-project-issues-dev] JFace Generics

On 08/29/2013 02:36 PM, Ed Merks wrote:
Not to rain on anyone's parade, but respectfully suggest the platform team should reconsider the gain verses the client impact for generifying the JFace APIs.   Designing generic containers isn't easy, and it's all too easy to make mistakes that will be difficult to correct in the future
In the end, many of the things being changed are effectively SPI.  One implements the APIs for providers and passes them to a generic container that does the right things with it.  There's little to be gained from adding generics, to justify the cost to the ecosystem, and getting it right is much harder than it appears at first glance...
Although I trust people saying that adding generics is difficult and error-prone (<T> or <? extends T> ?), I believe that adding generics in JFace has a lot of value, simply because of the number of cast necessary when dealing with a ContentProvider/LabelProvider couple. Dealing with current APIs forces us to remind the actual types for the JFace viewer, and it is a tricky exercise that is error prone: I've often seen/written some ClassCastException that takes more time to notice and debug that if I could see immediate feedback in IDE thanks to generic.
Overall, adding generics to JFace will really boost productivity of JFace users. That's IMO a valid reason to introduce warnings on existing code.

What is the current issue? Is it that existing code using JFace will now show warnings? Is this really an issue, does it prevent code to work? I don't think so. Those warnings just reveals that current usages of JFace don't leverage this new smart mechanism to prevent from ClassCastException. It's not a big deal to see them.
IMO, just asking to roll back everything is just like disabling a FindBugs rule: it doesn't solve anything, it just hides a place for improvement. In the end, it reduce code quality.

So, IMHO, the balance is more in favor of adding generics that in many cases will provide a better productivity and quality.
And I think it is totally fine to start merging such change so early in the release train to get maximal feedback.

I see (in Gerrit; thanks Matthias) that you've committed changes for TreeViewer and here I think the whole approach is completely questionable.  When is it the case that a tree view has uniformly the same elements throughout?   I think that's so rarely the case that it's worse than useless to make such an assumption; I would argue it's mostly just noise that will never solve real problems.

I've seen many TreeViewers using a super type other than Object, especially in the modeling world, where almost everything is an EObject (and often a specialized super-type shared across the whole metamodel), or in some JDT or PDE code where there are some TreeNodeAdapter (or whatever pattern which create a dedicated type to put in TreeContentProvider). So it seems to make sense for TreeViewers as well. And for other cases, it's not a big deal to write "TreeContentProvider<? extends Object>".
Mickael Istria
Eclipse developer at JBoss, by Red Hat
My blog - My Tweets

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