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" <[email protected]> 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 <[email protected]> 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 <[email protected]
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" <[email protected]> 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
