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

Mon Feb 18 21:43:17 EST 2013

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."
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