From: "Hartin, Brian" <Brian.Hartin@...>
Date: 2008-04-02T02:21:26+09:00
Subject: Does Ruby support exception wrapping (exception chaining)?

I could not find any information about this, except regarding DRb.

It seems like the raise method / Exception class ought to allow me to
pass in a 'causal' exception, e.g.

begin
  foo
rescue Exception => e
  raise ServiceNotFoundException, "The service could not be contacted",
e
end

This doesn't work.  I can, however, pass in the backtrace, e.g.

raise ServiceNotFoundException, "The service could not be contacted",
e.backtrace

However, doing this I get the stack trace but not the type or message
from the causal exception (unless I manually put them in the message
string).  Ideally, I'd be able to use exception chaining such as in
Java, in which my stack traces include causal exceptions:

WebServiceCommunicationException: The WSDL could not be obtained from
http://blah/wsdl.
  from (webservice_client.rb):123:in `obtain_wsdl'
  from (webservice_client.rb):12:in `request_price'
caused by ParsingError: Unexpected element 'html'
  from (other_class.rb):234 in 'some_method'
  from (other_class.rb):23 in 'some_other_method'
  ...

including a 'cause' field on the Exception class, e.g. e.cause.

Is there some reason why this would not fit the Ruby style?  If not, is
this something that would be considered as a patch/change for Ruby?

I realize I could probably monkeypatch Exception, but this seems (to me)
like it would be an improvement to the language.

Thanks,

Brian Hartin
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