I don't think this is something we can state outright. If I
BeanManager.fireEvent("some string"); then it's not mutable.
On Thu, Dec 18, 2014 at 3:03 AM, Jozef Hartinger <jharting(a)redhat.com>
wrote:
On 12/17/2014 05:49 PM, Antoine Sabot-Durand wrote:
Ok guys,
Let’s do it again. I didn’t say we have to forbid the mutability I said
we have at least to explicitly write that it’s mutable
Agreed.
and seriously think of having it immutable for event fired asynchronously.
I agree that we should have a discussion about pros/cons. From what I saw
working on a fireAsync prototype to me the possible benefits of allowing
immutable events only are not worth the limitations.
(Pete) I don’t think it’s specified. As objects are, by default in Java,
mutable, I would assume that payloads are implicitly mutable.
Sorry @Pete I don’t agree with your point. Yes, in Java object are
mutable but firing an event is not a standard Java feature : you send your
object to a black box and let this box dispatch your object to listeners
transforming one call to multiple call : it’s far from standard Java rules.
Even if it’s not written it’s an observer pattern and there are people out
there thinking that introducing mutability in observer is an anti-pattern
since some listener will receive a different payload than the one that was
sent to them.
It’s like making a method call and having no guarantee that the parameter
received in the callee has the same value that in the caller...
I won’t start discussion on bad practice or anti pattern as I also use
mutability in event but there as much reason for user to assume their
payload will be mutable than the other way around.
I can assure you that when I give a talk on CDI, this payload mutability
is often a surprise for attendees...
(Romain) why isn't it portable?
So yes @Romain it’s not portable (in theory of course, since both
implementations support mutability). Someone could write a CDI
implementation with event payload immutability without any issue with the
spec and TCK.
Most of you are so dependent of this feature that you only reacted to
the idea or forbidding it (which wasn’t the content of my mail) ;). So we
all agree that it’s an important feature. Therefore what’s the issue to
specify this mutability and add TCK test for it ?
Now I don’t deal with that subject for nothing, we are planning to
introduce Async events. I think that it’ll bring extra complexity if we
support mutability in async events. And even if I’m wrong and we finally go
for mutability in async events, this will lead to possible side effect
(lock) that could have impact on perf, so it should be explicitly written
IMO.
Antoine
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