From: Robert Klemme <bob.news@...>
Date: 2005-10-19T16:57:06+09:00
Subject: Re: Catch/throw vs rescue/raise/retry

Edward Faulkner wrote:

> On Wed, Oct 19, 2005 at 07:07:05AM +0900, Warren Seltzer wrote:
> > There appear to be 2 separate exception mechanisms in Ruby,
catch/throw and
> > rescue/raise/retry.  Is this right?
>
> Yes, but they're not used for the same thing.
>
> rescue/raise is used to signal error conditions.  This is analogous to
> Exceptions in Java or C++.
>
> Throw/catch is used to unwind the stack to a desired point.  It's like
> a labeled break.  For example:
>
> catch(:done){
>   loop {
>     do_work
>     if time_to_stop? throw :done
>   }
> }

You probably meant

catch(:done){
  loop {
    do_work
    throw :done if time_to_stop?
  }
}

> It's nice because you can break out of arbitrarily nested
loops/blocks/etc.

Plus you can return something from the throw like this:

catch(:done){
  loop {
    do_work
    throw :done, "result" if time_to_stop?
  }
}

Kind regards

    robert