Value equality (was: Value types questions and comments)

[John Rose]

On May 16, 2016, at 8:29 PM, Kevin Bourrillion <kevinb at google.com> wrote:
> 
> And by "deep equals" I mean equivalent behavior to
> 
> https://docs.oracle.com/javase/8/docs/api/java/util/Arrays.html#deepEquals-java.lang.Object:A-java.lang.Object:A- <https://docs.oracle.com/javase/8/docs/api/java/util/Arrays.html#deepEquals-java.lang.Object:A-java.lang.Object:A->
> 
> at least that is what AutoValue has been doing.

To the extent I understand this, it seems wrong:  deepEquals treats arrays as if they are lists, which is an abstraction shift.  Surely you aren't suggesting cracking a component reference in a subfield and treating its object as a List of its components, and so on recursively?  Because that's what deepEquals does.

Or do you mean that, just as deepEquals avoids using op==(ref,ref) on array components, so "deep equals" should avoid using op==(ref,ref) on value components?

You can avoid op==(ref,ref) by replacing it by a call to ref.equals(ref), or you can avoid op==(ref,ref) by cracking the refs and recursing.  That latter breaks an abstraction, so I think we agree it's bad, but *that* is a more "equivalent behavior" to Arrays.deepEquals.

— John