From: Sean O'Dell <sean@...>
Date: 2004-06-15T07:59:11+09:00
Subject: Re: undefine

On Monday 14 June 2004 15:47, Mark Hubbart wrote:
> On Jun 14, 2004, at 2:58 PM, tony summerfelt wrote:
> > while(<binkd>)
> > {
> >     # date parsing code was here
> >      @diff=Delta_DHMS(@binkdate,@today) if /(\[\d+\])/;
> >      print $trimmed $_ if $diff[0] < $ARGV[1] && defined(@diff);
> >      next  if defined(@diff);
> >      print $trimmed $_ if ! /(\[\d+\])/;
> >      undef(@diff);
> > }
>
> testing whether diff is defined won't work in ruby anyway. Any time you
> have an expression like this:
>
>    foo = 23 if expression
>
> foo ends up being automagically defined anyway. After running that
> code, if expression is false, foo == nil.
>
> So, as Sean says, it would probably be better to use nil, unless
> Delta_DHMS might return nil itself.

Oh!  Which brings to mind something really neat I figured out awhile ago.  If 
Delta_DHMS really can return nil as a valid value, try re-writing the code 
like this:

{
    # date parsing code was here
     @diff=Delta_DHMS(@binkdate,@today) if /(\[\d+\])/;
     print $trimmed $_ if $diff[0] < $ARGV[1] && @diff != :undefined;
     next  if @diff != :undefined;
     print $trimmed $_ if ! /(\[\d+\])/;
     @diff = :undefined;
}

Initialize @diff = :undefined in your class initialize method.  :undefined 
will be a Ruby symbol that gets created on its first use.  From there on out, 
just set @diff to :undefined whenever you need to "undefine" it.

	Sean O'Dell