From: Robert Dober <robert.dober@...>
Date: 2007-07-25T18:17:13+09:00
Subject: Re: Static variables in Ruby.

On 7/25/07, Robert Klemme <shortcutter@googlemail.com> wrote:
> 2007/7/25, Robert Dober <robert.dober@gmail.com>:
> > 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 :)
>
> The reason why it works is this:
>
> >> def f; (0..0).object_id end
> => nil
> >> 5.times {p f}
> 69868270
> 69868270
> 69868270
> 69868270
> 69868270
> => 5
Actually this is a reason why it should *not* work
def f; (0..0).object_id end
2.times{ p f }
p (0..0).object_id
Nevertheless it does because of the scope local optimization if I
understood Jo�l correctly.
>
> The Ruby interpreter optimizes this when both ends are constant.
>
> >> def g(a)(0..a).object_id end
> => nil
> >> 5.times {p g(1)}
> 69627090
> 69626930
> 69626820
> 69626680
> 69626560
> => 5
>
> Kind regards
>
> robert
>
>

Hmm as we are exploring it, let us see if it works for all constants,
somehow I doubt it...
Fixnum ranges work, Bignum ranges do not
646/146 > cat rang_oid.rb && ruby rang_oid.rb
#!/usr/local/bin/ruby
# vim: sw=2 sts=2 ft=ruby expandtab tw=0:


def f; "08%x" % (1..1073741823).object_id end
def b; "08%x" % (1..1073741824).object_id end

puts "f"
3.times{ puts f }
puts "b"
3.times{ puts b }
f
08..fdbeb46ae
08..fdbeb46ae
08..fdbeb46ae
b
08..fdbeb4366
08..fdbeb4334
08..fdbeb4302

So for bignums the values will not be kept.

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