From: "Jesús Gabriel y Galán" <jgabrielygalan@...>
Date: 2012-01-10T05:14:37+09:00
Subject: Re: Class instance variable question

On Mon, Jan 9, 2012 at 7:46 PM, Stefano Crocco <stefano.crocco@alice.it> wrote:
> Il giorno Tue, 10 Jan 2012 03:26:19 +0900
> Matt Mencel <MR-Mencel@wiu.edu> ha scritto:
>
>> Hi,
>>
>> I have this class (below) that takes a deeply nested hash and returns back
>> a new hash without all the nesting.  The problem I'm having is that it
>> seems to be that @all_values is not empty if I call it a second time from
>> my program.  First time is fine, but the next time I use
>> get_all_values_nested, @all_values still has the results in it from the
>> first time it was used.
>>
>> Any thoughts on what I'm doing wrong?  I just want @path and @all_values to
>> be empty each time I use the get_all_values_nested function.
>
> By definition, instance variables (including instance variables of class
> objects) keep their values until something else is assigned to them. If you
> need to access the values stored in @path and @all_values from somewhere
> other than gel_all_values_nested, but you want them empty in that method,
> then you'll have to do so yourself:
>
> class Tools
>
>  def self.get_all_values_nested nested_hash = {}
>    @path = []
>    @all_values = {}
>    # ...
>  end
>
> end

The problem there is that you lose the aggregation of path within the
recursive calls, since you are clearing at the beggining of each call.

> If those two variables are only needed from within the body of
> get_all_values_nested, then you should use local variables instead.

That's what I thought. If this is not the case, then the solution
should be different, but I'm not sure how those two requirements hold
up together: you need them empty before calling that method, but need
to read the resulting values in other cases. Also, I think path ends
up empty after the call, so maybe we are talking only about
all_values. If this is the case I would do it like this:

class Tools
  def self.get_all_values_nested(nested_hash={})
    @all_values = _get_all_values_nested(nested_hash)
  end
end

and use the definition for _get_all_values_nested that I propose in my
other email. The OP should clarify, but I don't think his use case
involves having memory of the computation within calls or something
like that.

Jesus.