Are value types supposed to work at all currently?

Peter Levart peter.levart at
Mon May 25 16:26:00 UTC 2015


I've been playing with the idea of Packed Objects over a weekend. Not 
hacking the VM like IBM, but using pure Java (with a little help from 
Unsafe ;-). Here's what I came up with:

It's interesting from the semantics standpoint alone. Mutating / viewing 
operations are possible to construct and compose in a generic way. 
Packed Objects are not value types, but can be used as value types. They 
can also be used to mutate parts of "values" in a well defined way. 
Additional features that come to mind besides those already implemented 
in above prototype are:
- read-only views of components of a packed object / array
- mapping native memory instead of heap as an option (like ByteBuffer)
- atomic operations on primitive components (CAS, GAS, GAA, ...)
- "view" locks - locking a range occupied by a component to allow 
exclusive accesses to a (sub/super)component.

Regards, Peter

On 05/21/2015 10:51 PM, Volker Simonis wrote:
> Hi Simon,
> it may be worth mentioning that there are other projects/approaches like
> IBM's PackedObjects or Gil Tene's ObjectLayout which solve at least a part
> of the problems which are addressed more generally by ValueTypes.
> I compared them in a talk that I was giving at FOSDEM (did we actually met
> there?) and JPoint:
> Incidentally I'll also give this talk tomorrow at JEE Conf in Kiev so if
> you should be around you're very welcome;)
> Regards,
> Volker
> On Thursday, May 21, 2015, Simon Ochsenreither <simon at>
> wrote:
>> Hi Brian, hi Maurizio,
>> here are the slides I used for my talk yesterday:
>> I hope they accurately reflected the current situation as much as possible.
>> Corrections and comments welcome! (The talk at ScalaDays will likely look
>> quite differently, though.)
>> I finished the slides a few minutes before the talk, so they are quite
>> rough.
>> One thing I would certainly add are all the boxing considerations, which
>> were discussed at the meetup, but are missing on the slides.
>> Thanks!
>> Bye,
>> Simon

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