From: Robert Klemme <bob.news@...>
Date: 2005-11-17T00:02:57+09:00
Subject: Re: static variable; behaviour in ruby?

Hugh Sasse wrote:
> 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.

I'm not yet convinced that it's actually so complicated.  Please see my
other posting.

    robert