[erlang-questions] Use of Records in the Java API

[Gleb Peregud]

On Wed, Jun 11, 2008 at 10:23 AM, Alexander Lamb
<alexander.lamb@REDACTED> wrote:
> Hello,
>
> My Erlang modules are mainly a server to Java Web applications (for
> the time being).
>
> This means that I am making a big use of the Erlang Java API which
> works fine.
> Since my Erlang modules use Mnesia to store data coming from the Java
> side (and vice versa), I need to implement functions with many
> parameters for example to insert new data in a Mnesia table.
> I also need to convert tuples into actual Java objects when reading
> data.
>
> This would be simpler if the Java API had an OtpErlangRecord. It would
> make it possible to subclass it and could even be the prefered way of
> bridging the Erlang world with the Java world. It would also avoid
> breaking code each time a new attribute is needed for a Mnesia table
> (making it today necessary to add a parameter to the complete chain of
> function calls).
>
> I didn't find any mention of OtpErlangRecord in the documentation. I
> suspect it is because the Java API was written before records were
> introduced in Erlang.
>
> In a more general sense, is there any plan to enhance the
> functionalities of the Java API  to handle more gracefully the
> mismatch between the loosely typed functional world of Erlang and the
> object oriented world of Java?
>
> I could very well imagine a Java class to handle marshalling and
> unmarshalling of terms at a high level using records. You would add a
> type description to the attributes and on the Java side you would
> immediately receive objects (subclasses of OtpErlangRecord for
> example). It could look somewhat like tools such as Cayenne or
> Hibernate in the SQL world.
>
> Just some thoughts. And since in two weeks Dennis Byrne is making a
> presentation at Erlang Exchange on that subject, maybe if Dennis is
> reading this post, he could consider preparing a few words in that
> direction for his London speech:-)
> That comment actually also applies if the client is in ActionScript
> for a Flash/Flex application or even JavaScript.
>
> Alex

Hello,

There's a problem with records on the Java side, since records are
comple-time module-specific features. As far i know erlang VM does not
have any runtime information about records, hence it is unable to send
it to Java side. Though probably it is not possible to implement
OtpErlangRecord in general way.

Feel free to correct me if i'm wrong.

Best regards,
-- 
Gleb Peregud
http://gleber.pl/

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