Shouldn't Optional be Serializable?

[Remi Forax]

On 09/18/2013 12:54 PM, Vitaly Davidovich wrote:
>
> Rémi,
>
> Sorry, using performance due to indirection and missed escape analysis 
> as reason for not making Optional serializable is just silly.
>

You miss the point here, it's not a bug or an issue with the escape 
analysis,
the reference escape, it's how the code is written if you declare a 
field Optional
so the boxing will be never removed by using escape analysis.
It's exactly like using a wrapper type instead of a primitive type when 
you declare a field.

and if you want to serialize a field which is Optional, there is no 
issue, mark it transient, use orNull() when serializing and
fromNullable() when deserializing, BTW it will be better if you decide 
that the field can not store null in a future version.

>   It's not going to prevent people from using this type as a field 
> (docs/guidance is a better way to steer people in the right direction).
>

Why not having both ?

This is IMO similar to what Martin Thompson calls mechanical sympathy, I 
prefer to live in a world
where the JDK API and the VM works in harmony.
Optional is nice from the API point of view, but not if you store it in 
a field.
If it's not something that should be stored in field, there is no point 
to make it serializable.

> Using your logic, may as well argue that no wrapper/datastructure 
> class be used at all that has a couple of impls and an interface/base 
> class.
>

no, the trade off is not the same.
If you use Optional for every fields, we already know that it doesn't 
work at all. Because this is how the VMs were working before 2000.

> And if JIT cannot remove the box for whatever reason, should we not 
> allow Optional at all? :)
>

If people don't want to see the trade off behind it, may be you're right,
but I think that the Java community is more mature than that.

> Cheers
>

Rémi

> Sent from my phone
>
> On Sep 18, 2013 2:41 AM, "Remi Forax" <forax at univ-mlv.fr 
> <mailto: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 <mailto: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
>             <mailto: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
>
>
>