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AspectJ and Encapsulation (was [aspectj-users] Q about "adviceexecution" and "declare error")
|
Kevin,
I think this discussion also belongs
on aspectj-dev.
You make a very good point. Most aspects
have a well defined purpose and those that "break encapsulation"
(I don't think they do but that is a separate conversation about
semantics) do so for a reason. If a private field/method needs to be accessed
(and there are plenty of good use cases for this) or a private method advised
a conventional approach would require the class author to add accessor
or template methods. In a large system this will involve several authors
and many classes. Besides the obvious code maintenance issue there is one
of integrity. With the traditional approach, which supposedly doesn't break
encapsulation, any Tom, Dick and Harry can call the new methods. With the
AspectJ implementation only the aspect has access.
Matthew Webster
AOSD Project
Java Technology Centre, MP146
IBM United Kingdom Limited
Hursley Park, Winchester, SO21 2JN, England
Telephone: +44 196 2816139 (external) 246139 (internal)
Kevin F <aj@xxxxxxxxxxxxxxxxxxxxxxx>
Sent by: aspectj-users-bounces@xxxxxxxxxxx
26/02/2007 16:13
Please respond to
aspectj-users@xxxxxxxxxxx |
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To
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cc
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Subject
| Re: [aspectj-users] Q about "adviceexecution"
and "declare error" |
|
Hi Eric,
I don’t mean to butt in on your conversation and may have missed some
of the leading conversation; however, I believe the point is this: is it
better to implement certain things by making changes throughout the base
implementation or to violate encapsulation so that the single concern can
be addressed in one place? I know that I’ve had my share of weeks
consulting on different projects where I joined the project and was tasked
to analysis exactly the crosscutting concerns addressed by AspectJ through
the use of elaborate scripts and manual intervention. In my consulting
(usually as the guy called in to rescue a train wreck), it has been common
place to a single change in more than 100 files.
Any technology can be misused. I can use JNI to circumvent encapsulation,
but it doesn’t mean that JNI should be removed from Java.
Kevin
From: Eric Bodden <eric.bodden@xxxxxxxxxxxxxx>
Reply-To: <aspectj-users@xxxxxxxxxxx>
Date: Mon, 26 Feb 2007 09:57:32 -0500
To: <aspectj-users@xxxxxxxxxxx>
Subject: Re: [aspectj-users] Q about "adviceexecution" and
"declare error"
Yes, it's exactly this view you mention which I meant. A proper component
can be deployed in whatever context. As long as this context adheres to
the component's component model, this component is known to work and moreover
the outside world can see nothing more but its interface. This is not true
for a program that is deployed in the context of a general AspectJ program.
The aspects can see and modify anything they like. A class/package/component
has no means of hiding implementation details and in fact a lot of aspects
rely extracting context information from directly inside those classes,
which is IMHO sometimes quite worrisome w.r.t. independent development
of both, aspects and base code.
Eric
On 2/26/07, Matthew Webster < matthew_webster@xxxxxxxxxx <mailto:matthew_webster@xxxxxxxxxx>
> wrote:
Eric,
>If you want to give static guarantees, it's just painful and that's
>what many people are worried about.
But you _can_ make static guarantees about the AspectJ program. What you
seem to be describing is the trouble with making such guarantees about
a Java program that is later deployed and executed as an AspectJ program.
My comment about reflection related to privileged aspects but again you
can make static guarantees unlike with reflection.
Matthew Webster
AOSD Project
Java Technology Centre, MP146
IBM United Kingdom Limited
Hursley Park, Winchester, SO21 2JN, England
Telephone: +44 196 2816139 (external) 246139 (internal)
"Eric Bodden" <eric.bodden@xxxxxxxxxxxxxx>
Sent by: aspectj-users-bounces@xxxxxxxxxxx
22/02/2007 20:29
Please respond to
aspectj-users@xxxxxxxxxxx
aspectj-users@xxxxxxxxxxx
Re: [aspectj-users] Q about "adviceexecution"
and "declare error"
On 2/22/07, Matthew Webster < matthew_webster@xxxxxxxxxx <mailto:matthew_webster@xxxxxxxxxx>
> wrote:
>
> Eric,
>
> I was aware of the work on open modules but have not read the papers
you refer to. Perhaps I should. However I do not believe any new controls
are necessary because Java in conjunction with a runtime modularity framework
like OSGi already provides sufficient mechanisms. This is why I am working
on AOSGi (http://www.eclipse.org/equinox/incubator/aspects/).
Oh, sounds interesting. I will have a look at it.
>
> >I know whole research communities which believe that not being
able to
> >guarantee any sort of encapsulation by far the largest problem
of
> >AspectJ.
> I not believe AspectJ breaks encapsulation any more than Java reflection.
Well, that might be true but a lot of people would say that reflection
is bad style for almost everything but a few distinct use cases, too.
If you want to give static guarantees, it's just painful and that's
what many people are worried about.
Eric
--
Eric Bodden
Sable Research Group
McGill University, Montréal, Canada
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--
Eric Bodden
Sable Research Group
McGill University, Montréal, Canada
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Unless stated otherwise above:
IBM United Kingdom Limited - Registered in England and Wales with number
741598.
Registered office: PO Box 41, North Harbour, Portsmouth, Hampshire PO6
3AU