ARM: preserve supressed exceptions due to throw in finally block

[Neal Gafter]

On Thu, Apr 8, 2010 at 12:44 PM, Joe Darcy <Joe.Darcy at sun.com> wrote:

> On 04/08/10 11:27 AM, Neal Gafter wrote:
>
>> Carlos-
>>
>> This has the same problem as the proposal for handling suppressed
>> exceptions
>> in ARM: we have no experience to suggest that this way of preserving
>> suppressed exceptions is usable in realistic programs.  This
>> software-engineering aspect of ARM language design seems to have been
>> largely ignored.  I think more study of such software engineering aspects
>> would be well advised before ARM or any extensions to it are moved into
>> the
>> jdk.
>>
>> Cheers,
>> Neal
>>
>> On Thu, Apr 8, 2010 at 2:55 AM, Carlos Costa e Silva <carlos at keysoft.pt
>> >wrote:
>>
>>
>>
>>
>
> I would expect such study to be able to commence in earnest after there is
> a version of ARM available in the JDK for people to play with.
>

It is unfortunate that such experience is not developed before being moved
into the jdk.  There have not even been any proposed guidelines for how to
program in the presence of this mechanism.  Such guidelines would not depend
on having a prototype, and could be analyzed for their compositional
properties before a prototype is committed to the JDK.  The complete absence
of such guidelines is most troubling and should signal a warning message
about the language construct itself.

Language features of course evolve and are tuned as people gain experience
> with them; this was true of generics I would expect this to be true of ARM
> too.
>

Generics prototypes were available for years before appearing in the JDK.
At least with generics we had a significant body of experience with their
use (yes, including wildcards) before the language construct appeared in the
jdk.  But in this case we do not even have the kinds of early programming
guidelines for the use of the construct in realistic software engineering
scenarios that we had for generics.

This reminds me a bit of the discussion surrounding erasure (vs
reification).  Some people who had a naive view of the problem thought we
were needlessly throwing away information, and "just" wanted us to preserve
it.  I jokingly offered to have the compiler email the erased type
parameters to them.  This is a joke because the information in that form is
useless to them.  Similarly, although we desire not to lose information
about "discarded" exceptions, there is no evidence that preserving them in
the way that is proposed will be useful except in very narrow
circumstances.  "Wait and see" isn't a very satisfying answer; we should
have more principled reasons to believe in a proposed solution.

Cheers,
Neal