From: Hugh Sasse <hgs@...>
Date: 2005-11-17T01:27:43+09:00
Subject: Re: static variable; behaviour in ruby?

On Thu, 17 Nov 2005, Robert Klemme wrote:

> Hugh Sasse wrote:
> > On Thu, 17 Nov 2005, Robert Klemme wrote:
> >
> >> Let's see whether I understand this correctly: you want your method
> >> "within" to create something that can be later thrown against the
> >> current line of the input and execute the given block only if the
> >> condition matches?  Wouldn't it be easier to just call within for
> >> each line of the input?
> >
> > all the statements in the input language which I'm processing with
> > instance_eval (for now) would be called for each line of the input.
> > So when each one that must hold state is called for the first time
> > it must clear the state, for future calls to that function on that
> > source line, but later input lines, it must not "cold start" the
> > state.

My use of "input" for supplied source code *and* data to process was
less than helpful.  Sorry about that.
> >
> > For within(), I'm trying to model sed's '/this/, /that/ { do_this}'
> > And I could have several withins in the same chunk of input
> > language.
> 
> I think I start getting a better understanding of your issue.  How about:
> 
> def within(*a, &b)
>   my_state = (Thread.current[:within] || = {})[a] ||= WithinState.new(a,b)
>   my_state.feed(current_line)
> end
> 
> If you want to make this safe against multiple invocations with similar
> parameters you might use another identifying thing (possibly invoking
> caller to determine source code location).

Yes, I was looking for that: I'd forgotten I could use caller in
something eval'd.   

Making it thread local means it outlives the scope of def and is not
in the normal global namespace.  That's a neat idea.
I think this will do everything I want....
> 
> Instead of the thread local you could also use a global but IMHO this is
> cleaner.
> 
> HTH
> 
> Kind regards
> 
>     robert
> 
        Thank you,
        Hugh
> 
>