From: Robert Klemme <bob.news@...>
Date: 2005-11-17T01:47:17+09:00
Subject: Re: static variable; behaviour in ruby?

Hugh Sasse wrote:
> 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.

And it's thread safe and automatically GC'ed on thread termination. :-)

> I think this will do everything I want....

Cool!  Glad I could help.

Cheers

    robert