[cdi-dev] Subclassing?

[Pete Muir]

I'm happy to go with whatever you guys agree on here :-)

Marius, I guess you are the only dissenter now :-) WDYT?

On 18 Sep 2012, at 07:46, Mark Struberg wrote:

> Hi Stu!
> 
> +1, fully agree.
> 
> 
> LieGrue,
> strub
> 
> 
> 
> ----- Original Message -----
>> From: Stuart Douglas <stuart.w.douglas at gmail.com>
>> To: Mark Struberg <struberg at yahoo.de>
>> Cc: Pete Muir <pmuir at redhat.com>; Romain Manni-Bucau <rmannibucau at gmail.com>; "cdi-dev at lists.jboss.org" <cdi-dev at lists.jboss.org>
>> Sent: Tuesday, September 18, 2012 12:22 AM
>> Subject: Re: [cdi-dev] Subclassing?
>> 
>> 
>> 
>> Mark Struberg wrote:
>>> Not sure if the trick with the ThreadLocal would work (aside from being dog 
>> slow).
>>> A->B->A should all lead to decorator invocations. Is this the case 
>> with your impl? (B might be another Decorator or a simple Bean)
>> 
>> Depends if B is a normal scoped bean or not. I agree this is not ideal.
>> 
>> To be honest I think it may actually be better to tighten the 
>> requirements for intercepted/decorated beans to allow interception to be 
>> implemented via a proxy. The way the CDI 1.0 spec was written this was 
>> not really possible to do and still be spec compliant (although the TCK 
>> did not test this), but we could change to 1.1 spec to require all 
>> intercepted classes to meet the proxiability requirements.
>> 
>> Basically as I see it the pros/cons of each are:
>> 
>> Subclassing:
>> 
>> Pros:
>> 1. Can use reflection to read fields / bean can have public fields
>> 2. No proxiability requirement
>> 3. Constructor is only called once
>> 
>> Cons:
>> 4. Self invocation cannot be handled consistently
>> 5. Implementation is more complex
>> 6. For normal scoped beans the bean has to be proxied anyway, so there 
>> is no advantage
>> 
>> 
>> Proxying:
>> 
>> Pros:
>> 7. Consistent with all other interceptor behavior
>> 8. Self invocation works as expected
>> 
>> Cons:
>> 9. Bean must meet proxiability requirements (although you can get around 
>> this with JVM specific hacks)
>> 10. Constructor will be called twice
>> 
>> I do not consider 1. to be worth considering as a real advantage (public 
>> fields == yuck). Basically the only advantage that sub classing has is 
>> when you are dealing with a dependent scoped bean that would not meet 
>> the proxyability requirements. I think in this case adding a default 
>> constructor to enable the bean to be proxied is not a big deal.
>> 
>> Stuart
>> 
>> 
>>> 
>>> LieGrue,
>>> strub
>>> 
>>> 
>>> 
>>> 
>>> ----- Original Message -----
>>>> From: Stuart Douglas<stuart.w.douglas at gmail.com>
>>>> To: Mark Struberg<struberg at yahoo.de>
>>>> Cc: Pete Muir<pmuir at redhat.com>; Romain 
>> Manni-Bucau<rmannibucau at gmail.com>; 
>> "cdi-dev at lists.jboss.org"<cdi-dev at lists.jboss.org>
>>>> Sent: Monday, September 17, 2012 11:31 PM
>>>> Subject: Re: [cdi-dev] Subclassing?
>>>> 
>>>> 
>>>> 
>>>> Mark Struberg wrote:
>>>>>    The main difference we get from subclassing is that even 
>> 'internal
>>>> invocations' (contrary to 'external invocations') will 
>> invoke the
>>>> decorator method
>>>>>    example
>>>>> 
>>>>>    public Class A implements X {
>>>>> 
>>>>> 
>>>>>       public void methA() {..}
>>>>>       public void methB() { methA(); }
>>>>> 
>>>>>    }
>>>>> 
>>>>>    @Decorator
>>>>>    public class Adecorator implements X {
>>>>>       @Inject @Delegate X x;
>>>>> 
>>>>>       public void methA();
>>>>>    }
>>>>> 
>>>>>    If we do _not_ apply subclassing but proxying, then invoking 
>> methB will NOT
>>>> trigger methA from Adecorator.
>>>>>    If we DO force subclassing, then a call to methB will also 
>> trigger the
>>>> decorator!
>>>>>    But that is contrary to all other EE proxying behaviour so far...
>>>> 
>>>> In weld we currently use a thread local to work around this, so self
>>>> invocation does not result in interceptors / decorators running again.
>>>> 
>>>> Stuart
>>>> 
>>>>> 
>>>>>    LieGrue,
>>>>>    strub
>>>>> 
>>>>> 
>>>>> 
>>>>>    ----- Original Message -----
>>>>>>    From: Pete Muir<pmuir at redhat.com>
>>>>>>    To: Romain Manni-Bucau<rmannibucau at gmail.com>
>>>>>>    Cc: 
>> "cdi-dev at lists.jboss.org"<cdi-dev at lists.jboss.org>
>>>>>>    Sent: Monday, September 17, 2012 5:58 PM
>>>>>>    Subject: Re: [cdi-dev] Subclassing?
>>>>>> 
>>>>>>    Romain,
>>>>>> 
>>>>>>    I agree, we can't specify to use subclassing. Please take 
>> a look at
>>>>>>   https://github.com/jboss/cdi/pull/117 where I've tried to 
>> address
>>>> this, in
>>>>>>    terms of what effects people will see.
>>>>>> 
>>>>>>    On 17 Sep 2012, at 16:54, Romain Manni-Bucau wrote:
>>>>>> 
>>>>>>>      Hi,
>>>>>>> 
>>>>>>>      There is a bunch of jira to specify subclassing should 
>> be used in
>>>> some
>>>>>>    cases so i mail here instead of answering all jira.
>>>>>>>      IMO it is specifying too much the technical part:  
>> specify the
>>>> constructor
>>>>>>    should be called twice is better for a spec IMHO (but this 
>> case is not
>>>> logical
>>>>>>    at all ;))
>>>>>>>      Why this need?
>>>>>>> 
>>>>>>>      - Romain
>>>>>>> 
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