From: Joel VanderWerf <vjoel@...>
Date: 2008-04-03T03:58:58+09:00
Subject: Re: Does Ruby support exception wrapping (exception chaining

Brian Hartin wrote:
> Joel,
> 
> This doesn't really provide the main benefit to exception wrapping 
> mechanism:  the ability to wrap low-level exceptions in an appropriate 
> higher-level exception and yet not lose the entire stack trace, or the 
> types and messages of the low-level exceptions.  Exception wrapping 
> (a.k.a. chaining) in Java (a good model for this feature, I think) makes 
> the idea of a 'causal Exception' part of the class (via a 'cause' 
> field), and the stack trace: an Exception's stack trace includes the 
> causal 'chain' of Exceptions automatically.

How about this?

class ServiceNotFoundException < StandardError
   attr_reader :cause
   def initialize cause
     @cause = cause
   end
end

begin
   begin
     raise "foo"
   rescue Exception => e
     e2 = ServiceNotFoundException.new e
     raise e2, "The service could not be contacted: #{e.message}", 
e.backtrace
   end
rescue Exception => e_outer
   puts e_outer
   p e_outer.cause
   puts e_outer.backtrace.join("\n  ")
end

__END__

Output:

The service could not be contacted: foo
#<RuntimeError: foo>
wrapped-exceptions.rb:10


-- 
       vjoel : Joel VanderWerf : path berkeley edu : 510 665 3407