From: Lionel Thiry <lthiryidontwantspams@...>
Date: 2006-02-09T01:33:22+09:00
Subject: Re: What's the difference between copying and sharing in closure?

Sam Kong a �crit :
> Hello!
> 
> I read an interview article with matz about closure.
> (http://www.artima.com/intv/closures2.html)
> 
> He mentioned that Ruby's closure is a real closure like Lisp.
> Local variables are shared between a method and a closure.
> 
> <snip>
> local variables are shared between the closure and the method. It's a
> real closure. It's not just a copy.
> ...
> Yes, and that sharing allows you to do some interesting code demos, but
> I think it's not that useful in the daily lives of programmers. It
> doesn't matter that much. The plain copy, like it's done in Java's
> inner classes for example, works in most cases. But in Ruby closures, I
> wanted to respect the Lisp culture
> </snip>
> 
> 
> Can somebody help me understand what he meant?
> Closures in other languages are different from Ruby?
> And if possible, I want to see the *interesting code demos".
> 
> Thanks.
> 
> Sam
> 

Sharing closure in ruby:

class A
 attr_accessor :a
 def initialize
  @a = "value"
 end
 def test
  proc { @a }
 end
end

a = A.new
block = a.test
puts block.call # "value"
a.a = "changed value"
puts block.call # "changed value"


Copying closure in python:

class A:
	def __init__(self):
		self.a = "value"
	def test(self):
		return lambda a=self.a : a

a = A()
block = a.test
print block() # "value"
a.a = "changed value"
print block() # "value"


-- 
Lionel Thiry

Personal web site: http://users.skynet.be/lthiry/