[forge-dev] reflection to access classes in project dependencies

Lincoln Baxter, III lincolnbaxter at gmail.com
Mon Feb 18 23:16:29 EST 2013 

On Mon, Feb 18, 2013 at 10:07 PM, George Gastaldi <ggastald at redhat.com>wrote:

> What if we refactor the JavaParser API to it's optimal form ? We may adopt
> a different package to avoid conflict with what we got, maybe renaming to a
> standalone project, since it's very useful to other projects as well, I
> guess.
>
> Em 18/02/2013, às 23:44, "Lincoln Baxter, III" <lincolnbaxter at gmail.com>
> escreveu:
>
> I don't like it because it's not really optimal, but... I don't really see
> a better way forward that doesn't break every API we have.
>
>
> On Mon, Feb 18, 2013 at 9:43 PM, Lincoln Baxter, III <
> lincolnbaxter at gmail.com> wrote:
>
>> Well, I actually meant refactor the entire JavaParser so that the types
>> are immutable by default, but modifiable when desired by doing an intanceof
>> and cast. This would, as John said, be a fairly invasive, with a fair
>> amount of downstream API impact, since all users of these APIs would now
>> need to reference these new types instead. It would mean refactoring all of
>> Forge.
>>
>> So from the perspective of Migration, it probably makes sense to do
>> something like add a method "isEditable()"
>>
>>
>> On Thu, Feb 14, 2013 at 2:19 PM, Thomas Frühbeck <fruehbeck at aon.at>wrote:
>>
>>>  If I understood Lincoln correctly, he meant adding an interface
>>> EditableJavaSource, so no change in the existing implementations necessary.
>>> So the boolean is substitutable by instanceof, your graceful error
>>> handling would be supported.
>>>
>>> Am 14.02.2013 20:10, schrieb John Franey:
>>>
>>> I would follow my object-oriented instinct to agree that a
>>> editable/non-editable parallel of the model would make sense.  After all,
>>> an editable java source is kind of a non-editable java source, and adds
>>> editing behavior.....
>>>
>>>  However, the parallel model seems to be a significant undertaking, and
>>> has a negative characteristic, in my opinion.   Lets say there exists a
>>> method to search for and return a JavaClass, editable or not.  In a use
>>> case where the JavaClass is to be modified, this method is inadequate. 1)
>>>  The caller would have to check if the result is instance of
>>> EditableJavaClass, then cast, or 2) an alternate query method would be
>>> provided to return only EditableJavaClass and since methods cannot be
>>> overridden by return type the alternate query method would have to be
>>> defined in a different interface.  Not taht either of these are difficult
>>> to overcome, but I think the parallel model would increase overall
>>> complexity a little and add to the level of effort, and the benefit gained
>>> is merely type protection against the runtime error of attempting to modify
>>> a non-editable java component.
>>>
>>>  To go against that impulse just a second, consider the option of a
>>> property on the base class, a boolean: editable.  This would avoid the
>>> parallel model, avoid casting and support polymorphic calls.   The runtime
>>> error of attempting to modify a non-editable component can be handled in a
>>> few different ways: 1) a runtime exception, 2) a quiet no-op.  Without the
>>> editable property, I would not use a runtime exception.  There would be no
>>> chance for the forge plugin programmer to avoid the error gracefully.  With
>>> the property, the error is the programmer's and a runtime exception could
>>> be appropriate.
>>>
>>>  Regards,
>>> John
>>>
>>>
>>>
>>> On Thu, Feb 14, 2013 at 1:11 PM, Lincoln Baxter, III <
>>> lincolnbaxter at gmail.com> wrote:
>>>
>>>>  As I understood it, we need a way of explicitly noting when a
>>>> JavaSource instance is mutable or not. Perhaps splitting the API into a
>>>> JavaSource an EditableJavaSource parallel.
>>>>
>>>>  It was also my understanding that proxies were going to be used to do
>>>> lazy-classloading for any JARs brought in via this system. I'm not sure we
>>>> need to worry about this just yet. We can get it working then think about
>>>> performance implications.
>>>>
>>>>
>>>> On Thu, Feb 14, 2013 at 12:23 PM, John Franey <jjfraney at gmail.com>wrote:
>>>>
>>>>>  I have no intention of providing a way to modify the class
>>>>> definition of a java class defined within a dependency of the user's
>>>>> project.
>>>>>
>>>>>  Putting the question another way:
>>>>>
>>>>>  To date, the forge java model today supports only modifiable java
>>>>> components.  This effort introduces non-modifiable java components to the
>>>>> forge java model.   This raises the question:  Would the non-modifiable
>>>>> java components be inspected with the same api that supports the modifiable
>>>>> java components (JavaClass, and others).  If no, what api is used to
>>>>> inspect the non-modifiable java components?
>>>>>
>>>>>  My naive answer is: the non-modifiable java components would be
>>>>> inspected using the same api as the modifiable java components.  Methods of
>>>>> that api that expressly modify the java component would be inert for
>>>>> non-modifiable java components.
>>>>>
>>>>>  John
>>>>>
>>>>>
>>>>>
>>>>> On Thu, Feb 14, 2013 at 12:05 PM, Thomas Frühbeck <fruehbeck at aon.at>wrote:
>>>>>
>>>>>>  Hmm, I expect loading of JARs not to the problem, is it? So the
>>>>>> loading and reflecting on the "external" class should be possible.
>>>>>> I was thinking of the next step, implementing kind of writable
>>>>>> JavaClass not just ignoring the changes, but making the modified class
>>>>>> available to the project.
>>>>>> Sorry if I misunderstood your quest? =)
>>>>>>
>>>>>> Thomas
>>>>>>
>>>>>> Am 14.02.2013 17:37, schrieb John Franey:
>>>>>>
>>>>>> Thomas,
>>>>>>
>>>>>>  I have minimal exposure to proxy due to experience with hibernate,
>>>>>> but my understanding is not adequate to understand how they would apply.
>>>>>>  Do I understand correctly that the benefit of a dynamic proxy is high when
>>>>>> a temporary class implementation is needed, and when a method of the proxy
>>>>>> is invoked, some action is taken, perhaps instantiating another
>>>>>> implementation of the interface.  In this use case, we don't need to invoke
>>>>>> the methods of a project's class, we need to inspect the methods (and other
>>>>>> members) of the class, right?
>>>>>>
>>>>>>  John
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>> On Thu, Feb 14, 2013 at 11:22 AM, Thomas Frühbeck <fruehbeck at aon.at>wrote:
>>>>>>
>>>>>>>  exactly what I was looking for :-))
>>>>>>> Thanks George!
>>>>>>>
>>>>>>> Am 14.02.2013 16:55, schrieb George Gastaldi:
>>>>>>>
>>>>>>> Hi Thomas,
>>>>>>>
>>>>>>>  Have a look in Forge 2.0 source code. We're using javassist at
>>>>>>> it's best in the proxy module
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> Em 14/02/2013, às 13:53, Thomas Frühbeck <fruehbeck at aon.at>
>>>>>>> escreveu:
>>>>>>>
>>>>>>>   Hi John,
>>>>>>>
>>>>>>> my two cents:
>>>>>>>     - this feature is a must-have, if Forge should be more than a
>>>>>>> tool to iniitialize projects, really great idea
>>>>>>>     - being pragmatic I would say this calls for proxy classes,
>>>>>>> similar to CDI decorators or the copy-on-write strategy
>>>>>>>
>>>>>>> (AFAIK the downside to CDI decorators is that they need interfaces
>>>>>>> on the base classes, thus again requiring changes of the classes if they
>>>>>>> hadnt been designed for it firstplace.)
>>>>>>>
>>>>>>> I have a very similar problem I am currently trying to solve with
>>>>>>> silly wrapper classes and was starting to think about dynamic proxy
>>>>>>> generation - unfortunately I have _no_ experience with such technology
>>>>>>> other than being simple user :-/
>>>>>>>
>>>>>>> Have you thought about javassist? Is it an option at all?
>>>>>>>
>>>>>>> Thomas
>>>>>>>
>>>>>>>
>>>>>>> Am 14.02.2013 16:21, schrieb John Franey:
>>>>>>>
>>>>>>> My motivation for this email is to satisfy FORGE-773.  However, this
>>>>>>> is also related to FORGE-563 and FORGE-424, and resolution could enable
>>>>>>> other features.
>>>>>>>
>>>>>>>  I have written a prototype:
>>>>>>> 1) an implementation of the forge java api interfaces which
>>>>>>> delegates to java's reflection, offering a read only perspective of java
>>>>>>> components.
>>>>>>> 2) a forge module, currently a facet, to search for a given binary
>>>>>>> class in the project's dependencies and returns the result wrapped in the
>>>>>>> above delegate.
>>>>>>>
>>>>>>>  These are demonstrable in a unit test.
>>>>>>>
>>>>>>>  My dilemma now is how to integrate these into the forge project.
>>>>>>>  There are a few different areas, but I'll start with this:
>>>>>>>
>>>>>>>
>>>>>>>  For some callers, a java class is a java class, whether it
>>>>>>> originates as source code (from the current forge project) or is a class
>>>>>>> from the dependency set.  For example, scaffolding primarily is a read only
>>>>>>> operation.  In this use case, it would be simpler for these clients to have
>>>>>>> a single interface to resolve classes because whether a class is source or
>>>>>>> binary is not relevant to the use case.
>>>>>>>
>>>>>>>  On the other hand, there is a set of classes in a user's project
>>>>>>> that are modifiable.  In these cases, a java class is not a java class.
>>>>>>>  Forge components might want the distinction somehow.  There ought the be
>>>>>>> some distinction of which class is modifiable and which is not.
>>>>>>>
>>>>>>>  Naively, I took the first thinking that the existing forge java
>>>>>>> model would be adequate.  To have separate java api for read-only and
>>>>>>> read-write java model objects seems a fundamental addition to the java
>>>>>>> model which requires much more effort.  In absence of such a model, I
>>>>>>> though to implement 'no-op' for those code changing methods  (e.g.,
>>>>>>> Named.setName() would be inert).  I assumed that forge component that
>>>>>>> change source code would have necessary context to know when it is
>>>>>>> operating on a source code module, avoiding attempts to modify a binary
>>>>>>> class.
>>>>>>>
>>>>>>>  So, I'm looking for discussion and consensus on the above.  Any
>>>>>>> thoughts?
>>>>>>>
>>>>>>>  Regards,
>>>>>>> John
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
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>>>>
>>>>
>>>>  --
>>>> Lincoln Baxter, III
>>>> http://ocpsoft.org
>>>> "Simpler is better."
>>>>
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>>
>> --
>> Lincoln Baxter, III
>> http://ocpsoft.org
>> "Simpler is better."
>>
>
>
>
> --
> Lincoln Baxter, III
> http://ocpsoft.org
> "Simpler is better."
>
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-- 
Lincoln Baxter, III
http://ocpsoft.org
"Simpler is better."
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