A disclaimer or two for Optional

[Joe Bowbeer]

Remi: Integer.valueOf is defined to return singletons for a range of values
near zero, and new instances in other cases. Java programmers understand
what this means, and their code sometimes depends on it.
On Oct 20, 2013 5:52 AM, "Remi Forax" <forax at univ-mlv.fr> wrote:

> On 10/20/2013 03:32 AM, Joshua Bloch wrote:
>
>> Brian,
>>
>>
>> On Sat, Oct 19, 2013 at 3:17 PM, Brian Goetz <brian.goetz at oracle.com<mailto:
>> brian.goetz at oracle.com**>> wrote:
>>
>>     OK, here's some of the background you may be missing.
>>
>>     "A future version of Java" will almost certainly have support for
>>     "value types", "user-defined primitives", "identity-less
>>     aggregates", "structs", or whatever you would like to call them.
>>      Without making promises or projections or even going into anTy
>>     details, this is high on the priority list, and some nontrivial
>>     analysis has already been done on what it might look like and what
>>     the migration compatibility concerns would be.
>>
>>
>> That's great because, frankly, Java's type system is way too simple.  I'm
>> glad you guys are investigating ways to make it more complex, and to
>> provide additional ways to do things that people are already doing. This
>> will keep Java programmers on their toes, which, frankly, is just what they
>> need.
>>
>> Josh
>>
>
> Hi Josh,
>
> It's a consequence of the introduction of auto-boxing/unboxing.
> When you call Integer.valueOf() you explicitly say that you don't care
> about the identity of the returned object, only the wrapped value is
> important.
> As you know, you can not predict the result of Integer.valueOf(x) ==
> Integer.valueOf(x), which means that == on Integer is meaningless.
>
> Currently, the code that try to remove boxing in the VM is full of special
> cases because the semantics of boxing is not the same for each wrappers
> (and is also partially specified in each Wrapper.valueOf). Recognizing that
> value types already exist in Java, and give them a proper documented
> semantics* is in my opinion a good idea.
>
> cheers,
> Rémi
> *by example, what is an array of value types is an interesting question.
>
>
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