From: "David A. Black" <dblack@...>
Date: 2008-07-21T05:23:17+09:00
Subject: Re: Does "rescue" wihtour argument handle any kind of Exception or not?

Hi --

On Mon, 21 Jul 2008, Phlip wrote:

>> Did you expect your program to do anything after printing "rescued !!!" ?
>
> Assuming you are addressing a senior enjinere, not a neophyte, yes I could 
> tell the difference between an interrupt and the rest of my program running. 
> It has major side-effects; I stuck the sample code at the top of my current 
> project.
>
> Curiously, this is what the original code was doing:
>
> begin
>  raise Interrupt
> rescue Object
>  p $!.class # sez Interrupt

I get ArgumentError with 1.8.6 and Interrupt with 1.9. I'm not sure
why Interrupt needs an argument in 1.8.6.

> end
>
> I didn't catch it either - 'raise' raises the given object, which here was 
> class Interrupt, and the metaclass itself of course does not inherit 
> StandardError.

raise doesn't necessarily raise the object itself. It looks for an
'exception' method on the object:

>> obj = Object.new
=> #<Object:0xb1bc>
>> def obj.exception; RuntimeError.new("Problem"); end
=> nil
>> raise obj
RuntimeError: Problem

Instances of Exception (and subclasses) return themselves from
#exception, so in that case you would be raising the object itself.
The classes return new instances of themselves.

>> r = RuntimeError.exception
=> #<RuntimeError: RuntimeError>
>> r.object_id
=> 287910
>> r.exception.object_id
=> 287910

If you give #exception on an instance a new message to deliver, and
you get a new instance:

>> r.exception("Problem").object_id
=> 268680


David

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