Generics & Reification Was Code Review Request: 7157893: Warnings Cleanup in java.util.* (original) (raw)

Stuart Marks stuart.marks at oracle.com
Fri Apr 13 01:33:52 UTC 2012

On 4/11/12 4:42 AM, Rémi Forax wrote:

On 04/07/2012 02:35 AM, Stuart Marks wrote:

In order to program effectively with generics, I think you have to understand erasure and its implications. It may have been an unfortunate choice, but erasure is part of the language and we have to deal with it and in some cases rely on it. I don't think it's merely an "implementation glitch." Erased casts are an implementation glitch, not the erasure by itself.

The difficulty I have with reification is that while there are proposals floating around for how it could be done, nobody really knows how it will eventually turn out, nor whether it will actually be done. If it is eventually done, there will legal and illegal constructs, constructs that generate warnings, and perhaps a style guide for how to use reified generics properly.

Right now, we can imagine what these future rules might be, but it seems untenable to me to try to make today's code conform to those imaginary future rules, especially in the absence of tools to help support those rules. There are several implementations that exist, here is the publicly available papers. M. Cimadamore and M. Viroli. Reifying wildcards in Java using the EGO approach. In SAC '07: Proceedings of the 2007 ACM symposium on Applied computing, pages 1315{1322, New York, NY, USA, 2007. ACM. M. Cimadamore and M. Viroli. On Rei cation of Java Wildcards. Science of Computer Programming, 2008

There's also Neal Gafter's blog post on the subject [1].

I haven't read these papers. Maybe I should just ask Maurizio about them. :-) I guess, is there enough commonality among all of these, and enough confidence that future-Java's generics reification will be similar to these, that today we should make coding style decisions based on future-Java?

I can sort-of see it if there's a choice to be made in circumstances like the following. Suppose we need to choose between a code fragments A and B where they're more-or-less equivalent in an erased world but B is clearly better in some future-Java world. Sure, we could choose B, I don't see the harm in it. I'm just not convinced that we know enough about future-Java to make a strong case for B.

s'marks

[1] http://gafter.blogspot.com/2006/11/reified-generics-for-java.html

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