Shouldn't Optional be Serializable?

[Remi Forax]

On 09/18/2013 07:32 PM, Pete Poulos wrote:
> One use case to consider here is RPC. many RPC frameworks use serialization
> to transmit the results of the RPC call over the network. If Optional is
> not serializable then you will be unable to return Optional results from
> methods invoked via RPC.

yes and no,
it depends how your RPC framework map errors because if you send an Optional
and then throw an exception in the client you will not have a meaningful 
stack trace.

Rémi

> On Sep 18, 2013 11:13 AM, "Joseph Unruh" <josephcu at gmail.com> wrote:
>
>> While It's clear that there are performance implications to using an
>> Optional field, keeping Optional non-serializable doesn't do much to
>> prevent that from happening. In the vast majority of cases, Optional will
>> be used in a non-serialized context. So, as preventative measures go, this
>> isn't a very effective one.
>>
>> Second, Optional exists primarily as a mechanism for marking that an object
>> may be null. This is a design objective. If the objective was performance,
>> then Optional wouldn't exist. Enforcing this usage on people, particularly
>> in the narrow context of serialization, is a premature optimization. If
>> it's useful to have optional exist at the API level in order to prevent
>> NPEs, why can't it be useful at the individual class level to prevent NPEs?
>>
>> Cheers,
>>     Joseph
>>
>>
>> On Tue, Sep 17, 2013 at 11:37 PM, Remi Forax <forax at univ-mlv.fr> wrote:
>>
>>> There is a good reason to not allow Optional to implement Serializable,
>>> it promotes a bad way to use Optional, at least from the VM point of
>> view.
>>> For the VM, Optional is a boxing, very similar to a boxing to Integer
>>> (in fact it's a little better because Integer.valueOf is badly* specified
>>> in the JLS
>>> but that's another story).
>>>
>>> so if you write:
>>> class Foo {
>>>    private Optional<String> description;
>>>
>>>    public Optional<String> getDescription() {
>>>       return description;
>>>    }
>>> }
>>>
>>> This implementation id bad for two reasons, the first one is that you
>> have
>>> to do
>>> a double indirection so will double your chance to have a value that is
>> not
>>> in the cache but in RAM when you want the underlying String.
>>> The second reason is that the VM will usually not be able to remove the
>>> boxing because the creation of Optional will be too far from the use.
>>>
>>> There is a better implementation
>>> class Foo {
>>>    private String description;  // warning nullable !
>>>
>>>    public Optional<String> getDescription() {
>>>       return Optional.fromNullable(**description);
>>>    }
>>> }
>>>
>>> It's the same API from the user point of view, but the creation of
>> Optional
>>> is in the same inline horizon that it's use if getDescription is inlined
>>> (and here given that the method is really small, the is a good chance).
>>> In that case the VM is able to remove the boxing and everybody is happy.
>>>
>>> So making Optional serializable goes in the wrong direction.
>>>
>>> cheers,
>>> Rémi
>>> * as we now now in 2013, it was less obvious when the decision was taken
>>> circa 2003.
>>>
>>>
>>> On 09/18/2013 03:16 AM, Pete Poulos wrote:
>>>
>>>> Optional holds data and while the vast majority of use cases for
>> Optional
>>>> will be to immediately pull the value out and do something, that doesn't
>>>> change the fact that it is still a data structure, somebody somewhere is
>>>> going to need to serialize it for some reason.  The other data
>> structures
>>>> in the java.util package are Serializable so making Optional
>> Serializable
>>>> makes things consistent.
>>>>
>>>> As far as I know the cost of adding Serializable to Optional is
>>>> negligible,
>>>> but the cost could be fairly significant to someone who needs to
>> serialize
>>>> it at some point and is unable to do so.
>>>>
>>>> Anyhow, I'm currently designing a set of functional (immutable,
>>>> persistent)
>>>> data structures for JDK8+ and I'm debating replacing my "Maybe" class
>>>> (functionally the same as Optional, but with Haskell's naming convention
>>>> for this data structure) the JDK8 Optional and I'm concerned that the
>> lack
>>>> of Serializable on Optional would cause problems for potential users of
>> my
>>>> API.
>>>>
>>>> I'm only using Optional/Maybe to wrap return values from methods so I
>> can
>>>> indicate missing/present values within my data structures, so I could
>>>> conceivably use Optional and still support serialization.
>>>>
>>>> Also, while we are having this discussion, is there an alternative to
>>>> serialization that is considered superior?  Over the years I have read
>>>> blog
>>>> posts by people condemning serialization, but I don't recall seeing any
>>>> alternatives suggested.
>>>>
>>>> Thanks,
>>>> Pete
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>> On Tue, Sep 17, 2013 at 5:32 PM, Vitaly Davidovich <vitalyd at gmail.com
>>>>> wrote:
>>>>   Presumably because you may want to have class fields that express
>>>>> nullability via Optional rather than null.  Whether that's a good
>> design
>>>>> or
>>>>> not is a separate question; conceptually, I don't see a reason why
>>>>> Optional
>>>>> cannot support that.  For "reference", Google Guava's version is
>>>>> serializable.  If someone were to replace their use with jdk's Optional
>>>>> then they will hit exceptions if the owner class is serialized.
>>>>>
>>>>> Sent from my phone
>>>>> On Sep 17, 2013 6:06 PM, "Remi Forax" <forax at univ-mlv.fr> wrote:
>>>>>
>>>>>   On 09/17/2013 11:44 PM, Pete Poulos wrote:
>>>>>>   Shouldn't java.util.Optional be Serializable?  Is there a good reason
>>>>>> for
>>>>>> it not be?
>>>>>>>   wrong question.
>>>>>> the right one is why do you want Optional to be Serializable.
>>>>>>
>>>>>>    Thanks,
>>>>>>
>>>>>>> Pete
>>>>>>>
>>>>>>>   cheers,
>>>>>> Rémi
>>>>>>
>>>>>>
>>>>>>