From: "Mauricio Fernández" <batsman.geo@...>
Date: 2002-10-08T19:08:08+09:00
Subject: Re: Specifying local and external block parameters (that old chestnut)

On Tue, Oct 08, 2002 at 06:31:03PM +0900, ts wrote:
> >>>>> "M" == Mauricio =?iso-8859-1?Q?Fern=E1ndez?= <Mauricio> writes:
> 
> >> b = 12
> >> 1.times { b := 2 }
> >> 
> >> `b := 2' will create a new block variable which shadow the previous
> >> variable  `b' 
> 
> M> matz said previously that in
> M> 	(0...10).each { |x| ... }
> M> the values would be assigned to x with ':=', that is, 
> M> 	x = ...
> M> inside the block would use the local. Put otherwise, this is the same as
> M> the "make them all local" solution w.r.t. block parameters!
> 
>  I know this, but you don't have || in my example.
>  
> M> i = 0
> M> x = 'some value'
> M> (0...10).each do |i|
> M>  x := 'surprise!' if i == 2
> M>  x = i # uses local after the := is run
> M> end
> 
> M> x => 1
> 
>  I don't see where is the problem
> 
> pigeon% cat b.rb
> #!./ruby
> i = 0
> x = 'some value'
> (0...10).each do |i|
>    x := 'surprise!' if i == 2
>    x = i # uses local after the := is run
>    p x
> end
> p x
> pigeon% 
> 
> pigeon% b.rb 
> ./b.rb:4: warning: shadowing variable `i'
> ./b.rb:5: warning: shadowing variable `x'
> 0
> 1
> 2
> 3
> 4
> 5
> 6
> 7
> 8
> 9
> "some value"
> pigeon% 
> 

Now I get it... it depends on whether Ruby sees ':=' in the *parsing*
phase. I thought Ruby would begin to consider variables local after
*executing* the ':=' statement. So I thought we'd get

i = 0
x = 'some value'
(0...10).each do |i|
   x := 'surprise!' if i == 2
   x = i # uses local after the := is run
   p x
end
p x
 
 
> pigeon% b.rb 
> ./b.rb:4: warning: shadowing variable `i'
> ./b.rb:5: warning: shadowing variable `x'
0
1
2
3
4
5
6
7
8
9
1
 
because after i == 2 only the local 'x' would be assigned to, not the
outer one. Of course this would be absolutely insane, but going the
syntactic way seems so much better :)


-- 
 _           _                             
| |__   __ _| |_ ___ _ __ ___   __ _ _ __  
| '_ \ / _` | __/ __| '_ ` _ \ / _` | '_ \ 
| |_) | (_| | |_\__ \ | | | | | (_| | | | |
|_.__/ \__,_|\__|___/_| |_| |_|\__,_|_| |_|
	Running Debian GNU/Linux Sid (unstable)
batsman dot geo at yahoo dot com

We come to bury DOS, not to praise it.
	-- Paul Vojta, vojta@math.berkeley.edu