From: Robert Klemme <bob.news@...>
Date: 2004-04-02T17:44:25+09:00
Subject: Re: error handling


"Mark Hubbart" <discord@mac.com> schrieb im Newsbeitrag
news:82DA4958-8456-11D8-97DE-000502FDD5CC@mac.com...
>
> On Apr 1, 2004, at 11:44 AM, Robert Klemme wrote:
>
> >
> > "Mark Hubbart" <discord@mac.com> schrieb im Newsbeitrag
> > news:789AB92E-83FE-11D8-97DE-000502FDD5CC@mac.com...
> >
> > [...]
> >
> >> This looks like a bug... sqrt() is recursing too deeply here, 1461
> >> levels seems a bit excessive. What values are causing it to dump like
> >> that? Could you give a specific example?
> >
> > I guess they are quite big so sqrt needs to many steps to identify the
> > square root.
>
> Oh. I hadn't realized that sqrt was supposed to recurse that much at
> all... even using two 60 digit numbers to create a Complex number to
> take the square root of, I couldn't get sqrt to cause me any problems,
> using 1.6.8...

That was just a wild guess.  I'd normally not expect sqrt to be written as
recursive function at all.  But the stacktrace seemed to indicate that.

> >> Normally, you could catch an error like this:
> >>
> >>    begin
> >>      0 / 0
> >>    rescue
> >>      puts "no dividing by zero in integer division!"
> >>    end
> >>
> >> .. but that doesn't work for me with a SystemStackError. I guess
those
> >> are always fatal errors.
> >
> > Works perfectly for me:
> >
> > irb(main):036:0> def rec; rec; end
> > => nil
> > irb(main):037:0> begin
> > irb(main):038:1*   rec
> > irb(main):039:1> rescue SystemStackError => e
> > irb(main):040:1>   puts "Caught it: #{e.inspect}"
> > irb(main):041:1> end
> > Caught it: #<SystemStackError: stack level too deep>
> > => nil
>
> Okay, that's kind of surprising. It works for me too, but only if I
> specify the error type like in your code... I tried it the other time
> in the same way as my example code above, and it failed. I thought that
> if you didn't specify the error type, it would catch anything;

I thought that once, too.  But I got wiser in the meantime. :-)

> apparently that's not the case.

"If you write a rescue clause with no parameter list, the parameter
defaults to StandardError."
http://www.rubycentral.com/book/tut_exceptions.html

Regards

    robert