From: Hugh Sasse <hgs@...>
Date: 2005-11-16T23:56:19+09:00
Subject: Re: static variable; behaviour in ruby?

On Wed, 16 Nov 2005, Robert Klemme wrote:

> Hugh Sasse wrote:
> > Any idea how to create or simulate a static variable in ruby?
> 
> I completely agree to Brian's comment.
> 
> > I want to create a variable to hold state between calls of a method,
> > but have the state disappear when the method goes out of scope.
> > I could create it in some external object but then I'd need to query
> > the scoping rules, and know where i was.
> 
> I'm not sure I understand you correctly here.  Why don't you just create
> an instance that holds this state plus whatever is needed and implement
> your behavior in a method of that class?  You can control the number of

Because I can't see how to call it into being correctly.  If I need
to know "when this method was called the first time" to do this,
then I need something with the same properties as a static variable,
in order to implement a thing with the same properties as a static
variable.

> scopes by the nuber of created instances.

But I need to know when to create them for the string I'm
evaluating, rather than when to call on existing ones in that string. 
> 
> Also, IMHO Pit has a valid point with his remark about a contradiction.

In ruby you can have several flip-flop expressions in the same
context...
> 
> > I'm trying to do an instance_eval on a string containing a method
> >    such as do_this x,y,z {block}
> > and I want to evaluate the block, or not, as a function of some
> > state against which x,y,z are compared.  The code will be called
> > several times, but I only want the state intialized the first time
> > the scope
> > is entered.
> >
> > And, just to make matters worse, there could be several independent
> > calls to this method within the scope, each with its own separate
> > state.
> >
> > Maybe there's another way to do this?
> 
> Did you consider using a Thread local stack for this (as I conclude from
> your latest posting nesting is possible)?

There is no concurrency in the thing at the moment, so I'm not sure
how to make use of that.  Maybe it is a design pattern I've missed.

I'm beginning to think it is nontrivial, and will probably to to use
gawk to avoid sed in this case.
> 
> Kind regards
> 
>     robert
> 
        Thank you,
        Hugh
> 
>