From: Jonathan Leighton <lists@...>
Date: 2006-03-01T11:42:05+09:00
Subject: Re: Iterators and Assigment

On Tue, 2006-02-28 at 22:38 +0900, Robert Klemme wrote:
> Godspeed wrote:
> > Consider...
> >
> > def fred
> >   yield $k
> >   puts "in fred #{$k}"
> > end
> >
> > $k=2
> > fred {|o| o = 3}
> > puts "outside fred #{$k}"
> >
> > produces:
> >
> > in fred 2
> > outside fred 2
> >
> > why is $k still 2 after the call to fred?
> 
> Because Ruby does call by value where values are object references.  Same
> holds for blocks and their parameters.  There is no implicit aliasing
> between k$ and o.  When the block is invoked you get a new reference which
> initially points to the same instance as $k.  Then you assign it and it
> points to some other object leaving $k still pointing to the old instance.
> 
> Kind regards
> 
>     robert

So, try this:

def fred
  $k = yield
  puts "in fred #{$k}"
end

$k = 2
fred { 3 }
puts "outside fred #{$k}"

Returns:

in fred 3
outside fred 3

You can call yield with parameters if you need the value of $k to be
accessible inside the block. Although $k is accessible inside the block
anyway as it's a global. Although you're probably not using a global in
your actual code.

Regards

-- 
Jonathan Leighton
http://turnipspatch.com/ | http://jonathanleighton.com/ | http://digital-proof.org/