A disclaimer or two for Optional

Joshua Bloch josh at bloch.us
Sun Oct 20 09:59:42 PDT 2013

Not premature optimization, but overspecification. That's true for all the
identity guarantees (String and boxed primitive). At most, they should have
been weak implementation suggestions. I'm astonished how much time is
wasted on trivial questions about the identity of these object references.


On Sun, Oct 20, 2013 at 9:44 AM, Remi Forax <forax at univ-mlv.fr> wrote:

> On 10/20/2013 06:09 PM, Brian Goetz wrote:
>> Right, which is why Integer is likely too far polluted to be rescued.
>> But, wouldn't it have been better if we could enforce that no one depended
>> on it in the first place?  Wouldn't it be a shame for Optional to join it
>> in the "hopelessly polluted by identity" department?
> JLS 5.1.7 is what is what is usually called a premature optimization.
> IMO the only sane choice is to just remove the wording about caching and
> performance and pretend that it has never existed.
> Rémi
>> On 10/20/2013 12:08 PM, Joe Bowbeer wrote:
>>> 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
>>> <mailto: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**>
>>>         <mailto: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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