From: Gennady Bystritsky <Gennady.Bystritsky@...>
Date: 2006-08-02T01:16:39+09:00
Subject: Re: I thought this was the one that worked?

Yes, it is:

class B
  def initialize(a)
    @a = a
  end

  def each
    yield # First block invocation

    @a.z = 77   # Changing the scope in 
    class << @a # which the block was created
      def puts(*args)
        $stderr.puts @z, *args.map { |_a| _a.upcase }
      end
    end

    yield # Second block invocation
  end
end

class A
  attr_accessor :z
  def f
    array = B.new(self)

### HERE'S YOUR FRAGMENT
    array.each do ||
      puts "Hello world!"
    end
### YOUR FRAGMENT ENDS HERE
  end
end

A.new.f

Procuces:

Hello world!
77
HELLO WORLD! 

Ruby does not assume what a method is going to do with a block, it just
creates a closure.

Gennady.

> -----Original Message-----
> From: Chad Perrin [mailto:perrin@apotheon.com] 
> Sent: Tuesday, August 01, 2006 3:32 AM
> To: ruby-talk ML
> Subject: Re: I thought this was the one that worked?
> 
> On Tue, Aug 01, 2006 at 06:15:10PM +0900, Just Another Victim 
> of the Ambient Morality wrote:
> > 
> >     Well, I think that meshes just fine with my take on it...
> >     To tell you the truth, I didn't expect you to ask me what my 
> > understanding of a closure is because I thought I had 
> already demonstrated 
> > it with the code sample I gave.  Of course, you're busy 
> digesting that and I 
> > appreciate it.  It means you're actually trying to 
> understand me (rather 
> > than just arguing at me.  Something that happens all too often...).
> >     If I may be so bold, I think that, perhaps, blocks 
> don't look like 
> > closures to you because you don't realize that methods that 
> take blocks, 
> > like "each," "inject," "collect," etc.. are methods (member 
> functions, if 
> > you're a C++ guy) and not arbitrary language constructs, 
> like "if," "while," 
> > "for," etc...
> 
> I'm not exactly a C++ guy.  I suppose I'm more of a Perl guy than
> anything else, judging by my familiarity with languages and the
> assumption of a lack of loathing (I'm as familiar with PHP as 
> with Perl,
> but I don't like it very much, for instance).  I am familiar with many
> of the idioms and much of the semantic and syntactic theory 
> of a lot of
> languages, even if I don't use them much, though.  The 
> dangers of doing
> consulting and industry analysis for money. . . .
> 
> 
> > 
> >     Now that I think about it, this whole argument can be 
> settled with one 
> > simple question.  If you doubt that all blocks are closures 
> then show us a 
> > counter-example.  Show us a "block" that is not a closure 
> and I will show 
> > you how it's not a block...
> 
> Is this a closure?  You tell me (and tell me how, if it is):
> 
>   array.each do ||
>     puts "Hello world!"
>   end
> 
> -- 
> CCD CopyWrite Chad Perrin [ http://ccd.apotheon.org ]
> print substr("Just another Perl hacker", 0, -2);
> 
>