From: Brian Candler <B.Candler@...>
Date: 2003-02-13T08:50:04+09:00
Subject: Re: Lexical scope and closures

On Thu, Feb 13, 2003 at 08:27:51AM +0900, Hal E. Fulton wrote:
> > Matz is thinking of changing the behaviour for a future version of Ruby as
> > follows:
> >
> > (1) block parameters are always locally scoped (so '|x|' in that example
> > will behave as if the outside 'x' did not exist, although a warning will
> be
> > printed because of the re-use of the name; but x will still be 0 after the
> > iterator has finished)
> 
> I didn't realize that. So we ARE breaking
> old code, eh?

Yes. That's one reason for the warning; the other reason is because Matz
finds the practice of 'shadowing' distasteful :-)

It will also break old code where it depends on a variable introduced in a
block being local, e.g.

   Thread.new {
     i = 0
     ... use i locally
   }

I don't remember seeing a warning for this situation being discussed, but it
would seem logical to do so.

What you gain: probably less surprising behaviour. "a = 0" always binds to
the method scope (whether or not it is inside a block), and "|a|" is always
block-local (whether or not 'a' has been used before).

Regards,

Brian.