From: Daniel DeLorme <dan-ml@...42.com>
Date: 2008-09-30T09:10:39+09:00
Subject: Re: ruby1.9 block scope

Nobuyoshi Nakada wrote:
> 
> At Tue, 30 Sep 2008 00:23:17 +0900,
> Daniel DeLorme wrote in [ruby-talk:316347]:
>>> My vague idea for the issue is that when you see the reference to a
>>> local variable inside of the block, the scope of the variable would be
>>> upgraded to the level of the reference.
>> Do you mean upgrade the scope of the variable dynamically? Is that even 
>> possible? I thought that all local vars had their scope pretty much set 
>> in stone at the lexical level. But if you could upgrade their scoping 
>> level dynamically... that would be nifty indeed!
> 
> I guess the parser would do it at the compile time.

That was also my guess; it least it's an easy concept to imagine. But it 
does bring the question of what to do when you *don't* want variables to 
"escape" into the enclosing scope? e.g.

class Foo
   defined_method :bar do
     x = 1  #I don't want x to be defined in the Foo scope
   end
   defined_method :baz do
     x = 2  #because it would wind up shared with this method
   end
end

The best I could think of was that a variable shouldn't be upgraded if 
the enclosing scope is a "class" or "module" section. That can be 
detected at parse time so it would work with lexical binding.

But it would be very interesting indeed if you could bind a block's 
variables to the enclosing scope dynamically. You could say:
   block.call_using_enclosing_scope #e.g. define_method
   block.call_using_own_scope #e.g. each

To me that feels very very powerful. And more power to the programmer is 
good, right? ;-)

--
Daniel