From: Sean Chittenden <sean@...>
Date: 2002-09-14T03:30:51+09:00
Subject: Re: Disabling exceptions - thoughts?

> |On #ruby-lang tonight, the topic of disabling exceptions came up.  In Perl, 
> |for example, you can temporarily (or permanately) disable particular (or all) 
> |warnings via a "no warnings" pragma.  I'm told CommonLisp also has something 
> |along these lines.
> |
> |Ignoring the "is it wise" for the moment, is it *possible* to disable 
> |exceptions in Ruby?
> 
> Not in the current implementation.  Besides we should define first
> what is going to happen on exceptional situation when exception is
> turned off.

You mean if the exception isn't being ignored?  It should be raised as
a normal exception would and left to the current stack.  You mean
something like a different exception or a possible bug?  Here's some
broken pseudo code that doesn't actually work, but illustrates the
idea:

Errno::EEXISTS.ignore do
  Dir.mkdir('/usr')
  Dir.mkdir('/usr/ports')
  Dir.mkdir('/usr/ports/databases')
  Dir.mkdir('/usr/ports/databases/postgresql-devel')
end

I know there are work arounds, but writing:

begin
  Dir.mkdir('/usr')
rescue Errno::EEXISTS
end

begin
  Dir.mkdir('/usr/ports')
rescue Errno::EEXISTS
end
etc...

gets tedious.  I know that in CL you can turn specific exceptions off
(thx matju) and that there are other ways to code this, but in short
hack scripts that system admins use/write, it's pretty nice to be able
to just disregard a specific exception.

Here's some more broken code to try and illustrate the idea:

class Exception
  def Exception.ignore(reraise_count = nil, &proc)
    exception_count = reraise_count.to_i
    begin
      yield(proc)
    rescue self.class
      exception_count -= 1 if exception_count.kind_of? Fixnum
      if reraise_count.nil? or reraise_count != 0
        # This implies that a proc object knows what instruction the
        # proc object left off on
        proc.resume()
      end
    end # begin
  end # def Exception.ignore()
end # class Exception

Just an idea.  -sc

-- 
Sean Chittenden