From: Phlip <phlip_cpp@...>
Date: 2004-10-20T03:44:19+09:00
Subject: Re: Question about closure

Sam Sungshik Kong wrote:

> Can somebody enlighten me?

In addition to the other (unread) answers:

            X = 42

            oval.bind('Button-1') {
                |event|
                doc(event)
                puts x.inspect()
                }

Ruby statements between { and } (or begin and end) form an object, called a
block, which passes into any method on its left. That method can evaluate
the statements inside the block immediately, and can store the block as an
object, called a Proc, so something can call it later. The block links to
instances of variables seen from functions around it, such as our x, even
after such functions return. Each instance of the block links to a parallel
instance of each variable, so such variables persist until the block itself
destroys. Languages such as Perl and Smalltalk also use these "block
closures".

They are more than a convenience: Variables must always have the narrowest
scope possible, and variables linked to a block, such as x, have the
narrowest conceivable scope over an indefinite lifespan.

-- 
  Phlip
  http://industrialxp.org/community/bin/view/Main/TestFirstUserInterfaces