From: Christopher Dicely <cmdicely@...>
Date: 2011-01-26T13:40:36+09:00
Subject: Re: Does Ruby support exception wrapping (exception chaining)?

On Tue, Apr 1, 2008 at 10:21 AM, Hartin, Brian <Brian.Hartin@pearson.com> wrote:
> 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?

You can certainly do a custom exception class that carries information
about a preceding triggering exception; the default handler won't do
anything with that information, though, but if you handle the
exception yourself, you can include the information with your output.
You can even include a method in your custom exception class to dump
the info so that client code can just call the method to get the error
report.
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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