From: "Hal E. Fulton" <hal9000@...>
Date: 2003-02-12T13:52:37+09:00
Subject: Re: Lexical scope and closures

----- Original Message ----- 
From: "Patrick Logan" <patrickdlogan@attbi.com>
Newsgroups: comp.lang.ruby
To: "ruby-talk ML" <ruby-talk@ruby-lang.org>
Sent: Tuesday, February 11, 2003 10:21 PM
Subject: Lexical scope and closures


> I read recently a flaw I did not previously know about...
> 
> "Blocks (closures) in Ruby do not introduce a new scope, only methods
> do.
> This is generally acknowledged as a flaw by the Ruby community but is
> left
> in for backwards compatibility.  For example:
> 
> x = 0
> [1,2,3].each{|x| print x}
> #x now equals 3"

I sympathize with you in a way, Patrick, but I
do find your choice of language a little strong.

I'm not certain it's "generally acknowledged as
a flaw" (nor where you are quoting).

There is certainly some disagreement as to how
some issues ought to be handled. Matz himself
has said he made mistakes in this area; I'm only
willing to consider something a true design flaw
when he says it is.
 
> Of course this is just wrong. I am hoping no one expects an
> implementation of Ruby to actually behave this way.

It surprised me at first, but I have had more than
three years to get used to it.

Don't make the mistake of thinking that the list
between the bars is like a method's formal parameter
list. There are some similarities. But it isn't a 
formal parameter list, never was, and (I'm guessing)
never will be.

For example, have you considered the fact that any
"assignable" entity can be placed there, for example,
a writable attribute?

  scrollbar = ScrollBar.new(...)
  (0..100).each {|scrollbar.percent| sleep(0.1) }

> Is it generally accepted that programs should not expect this? I would
> not be ashamed to break this code in a new implementation of Ruby.

As I said, I've gotten used to it. I do *sometimes* 
depend on this behavior, usually when I want to save
a value after a loop terminates normally or abnormally.
It's a minor thing, but it saves an extra variable.

Of course, it goes without saying that however Matz 
decides to reconcile all these issues, I will simply
learn it and live with it. I suppose we all shall.

Hal