Re-throwing an exception

Hi

Within Ruby, what is the proper way of re-throwing caught (rescued)
exception?

Is just using ‘raise’ after a ‘rescue’ proper? See below two attempts to
re-throw exceptions just using ‘raise’:

begin
    # Do stuff #
rescue ServiceException
    raise
rescue SdkException
    raise
rescue Exception => e
    raise SdkException.new( "Failed to process request: %s: %s" %

[e.class, e.message] )
end

Thanks

  • Jeff in Seattle

You can re-raise the rescued exception by calling raise with the
argument being the Exception (or subclass) object.

E.g.:

 begin
     # Do stuff #
 rescue ServiceException => e
     raise e
 rescue SdkException => e
     raise e
 rescue Exception => e
     raise SdkException.new( "Failed to process request: %s: %s" %

[e.class, e.message] )
end

Alternatively (same function, but coded how I’d have written it):

 begin
     # Do stuff #
 rescue Exception => e
     raise e if e.is_a?(ServiceException) || e.is_a?(SdkException)

     raise SdkException.new( "Failed to process request: %s: %s" %

[e.class, e.message] )
end

– Matma R.

Thank you for the reply

– Jeff in Seattle

this works too:
begin

Do stuff

rescue ServiceException,SdkException
raise
end

Hi Jeff,

While your exception code works, it’s not how you should use the “raise”
method in Ruby (you seem to be taking it from Java or so). The usual and
sensible way is

raise YourExceptionClass, ‘yourmessage’

This is less cumbersome and allows you to add additional arguments for
the call stack.

http://ruby-doc.org/core-1.9.3/Kernel.html#method-i-raise

Apart from that, you should be very careful when rescuing Exception
objects. That’s the most basic class which includes severe system errors
you shouldn’t touch at all.

The only situation where this might make sense is if you want to catch
all errors on the top level to execute some special code.

On Sep 20, 2012, at 14:21 , Jan E. [email protected] wrote:

While your exception code works, it’s not how you should use the “raise”
method in Ruby (you seem to be taking it from Java or so). The usual and
sensible way is

raise YourExceptionClass, ‘yourmessage’

This is true for raising, but he was asking about re-raising… in which
just calling raise is fine.

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