From: Robert Dober <robert.dober@...>
Date: 2007-07-25T20:20:10+09:00
Subject: Re: Static variables in Ruby.

On 7/25/07, dblack@wobblini.net <dblack@wobblini.net> wrote:
> Hi --
>
> On Wed, 25 Jul 2007, Robert Dober wrote:
>
> > On 7/24/07, Joel VanderWerf <vjoel@path.berkeley.edu> wrote:
> >> Nobuyoshi Nakada wrote:
> >> > Hi,
> >> >
> >> > At Tue, 24 Jul 2007 17:40:57 +0900,
> >> > Marcin Tyman wrote in [ruby-talk:261483]:
> >> >> Is any way to define static variables over function? As class static
> >> >> variables there is possible to define a static class variable as
> >> >> @@name_of_var. But I'm not sure if Ruby let define such variables in
> >> >> functions (like in C/C++)
> >> >
> >> >   def foo(x)
> >> >     (0..0).instance_eval{x,@x = @x,x}
> >> >     x
> >> >   end
> >> >   3.times{|i|p foo(i)} #=> nil, 1, 2
> >> >
> >> > The literal object can be Float, Regexp or Bignum, but Range
> >> > would be faster a bit.
> >> >
> >>
> >> Interesting. That is because Float, Regexp, and Bignum are instantiated
> >> per scope, right?
> >>
> >> Sometimes a little abstraction leakage can be useful!
> >>
> >> --
> >>        vjoel : Joel VanderWerf : path berkeley edu : 510 665 3407
> >>
> >>
> > I did not believe this,and why should I?
> > But it seems to be true ;)
> > def foo(x)
> > (0..0).instance_eval{x,@x = @x,x}
> > x
> > end
> >
> > 3.times{ |i| puts foo(i) }
> > (0..0).instance_eval{@x=42}
> > 3.times{ |i| puts foo(i) }
> >
> > Run this for a pleasant surprise :)
>
> I get the same result with or without the line between the two times
> calls.  Are you seeing it output 42?
No that is the pleasant surprise :)
If I understood the Guru Sans correctly that is because the
interpreter defines (0..0) scope locally -- the same object_id
notwithstanding -- amazing feature indeed.
Needless to say that one should rather not use it ;)

Cheers
Robert
>
>
> David
>
> --
> * Books:
>    RAILS ROUTING (new! http://www.awprofessional.com/title/0321509242)
>    RUBY FOR RAILS (http://www.manning.com/black)
> * Ruby/Rails training
>      & consulting:  Ruby Power and Light, LLC (http://www.rubypal.com)
>
>


-- 
I always knew that one day Smalltalk would replace Java.
I just didn't know it would be called Ruby
-- Kent Beck