From: "Daniel P. Zepeda" <daniel@...>
Date: 2003-02-09T16:32:01+09:00
Subject: Re: 'static' variables in a proc?

On Sun, 9 Feb 2003 14:51:23 +0900
ptkwt@shell1.aracnet.com (Phil Tomson) wrote:

> Is there a way to get a variable in a proc that maintains it's value 
> between different calls of the proc?
> 
> I tried using an instance variable:
>  p = proc { unless defined? @a
>               @a = 1
>             end
>             puts @a
>             @a+=1
>           }
> #<Proc:0x401bfdb0>
> irb(main):024:0> p.call
> true
> NameError: undefined method `+' for true
>         from (irb):22
>         from (irb):18:in `call'
>         from (irb):24
> 
> I'm not sure why @a became true...
> 
> Then I tried:
> 
>  p = proc{ unless defined? a
>              a = 1
>            end
>            puts a
>            a += 1
>          }
> 
> 
> ....and of course all I ever get out of it is 1, but at least a doesn't 
> become 'true'.

There's a couple of ways to do it, you could just define 'a'
outside the proc, this might suffice depending on what you're doing:

a = 0
p = proc { a += 1; puts a}

1.upto( 3 ) {
  p.call
}



a more general method would be to put 'a' in a singleton class:

require 'singleton'
class MyA
  include Singleton
  attr_accessor :a
  def initialize
    @a = 0
  end
end
q = proc { a = MyA.instance; a.a += 1; puts a.a}
1.upto( 3 ) {
  q.call
}


> 
> 
> Phil


-- 
Daniel P. Zepeda