From: Brian Candler <B.Candler@...>
Date: 2007-04-05T06:18:43+09:00
Subject: Re: A Syntax question..

On Thu, Apr 05, 2007 at 03:01:56AM +0900, Sonny Chee wrote:
> Hey Guys,
> 
> I would have thought the following two code snippets were equivalent.
> However, only the first one will raise err.  Can someone explain to me
> how I should be 'reading' the 2nd snippet?
> 
> 
>       rescue Exception => err
>         begin
>             RDoc::usage
>         rescue SystemExit
>         end
>         raise err
> 
> 
>       rescue Exception => err
>         begin RDoc::usage rescue SystemExit end
>         raise err

These are two different syntactic constructions.

       <expression1> rescue <expression2>

returns the value of <expression1>, unless there is an exception in which
case it returns the value of <expression2>

In this construct, you cannot specify the exception class. I think it only
catches StandardError and subclasses.

Typical usage:

     foo rescue nil                 #  just ignore StandardError

     a = foo rescue bar rescue baz  #  return value from foo, if exception
                                    #  then bar, if exception then baz

Regards,

Brian.