From: Charles Comstock <cc1@...>
Date: 2004-04-15T02:09:13+09:00
Subject: Re: Interesting Scoping Rules

David A. Black wrote:

> Hi --
> 
> On Thu, 15 Apr 2004, Charles Comstock wrote:
> 
> 
>>I guess I should have qualified my statement a little better, I did 
>>recognize that a def seems to be a hard scoping boundary, the question 
>>was much more that I was very suprised by this, and was curious if 
>>anyone had any insight as to WHY ruby chose to work things like this?
> 
> 
> I think it's generally true that local variable scope changes every
> time a new 'self' takes over:  
> 
>   class X
>     # self is X
>     def blah
>       # self is any instance of X
>     end
>     # self is X again, back to where we were
>   end
> 
>   class X
>     # self is X but we've backed out of the class and
>     # come back in, so we have a new local scope
>   end
> 
> The design is flexible: you can use #define_method instead of def, if
> you want to avoid changing self and therefore starting a new local
> scope.  
> 
> 
>>It suprises me much in the same way that we cannot def inside a def, it 
>>will result in a new def at the top scope.  It also suprises me in the 
>>way that if we stick a class inside of a class instance variables will 
>>not bubble down into the inner class.
> 
> 
> I'm not sure what you mean by that last one -- can you illustrate?
> 
> 
> David
> 

class A
   var = "me"
   class B
     puts var
   end
end

It's essentially the same rule that causes

   var = "me"
   class B
     puts var
   end

alone not to work I suppose.  The other complaint was that

def a
   def b
     puts "a"
   end
end

b

will result in
"a"

as opposed to getting a name error on b

also curious is that

class A
   @a = "me"
   class B
     puts @a
   end
end

results in
nil

again class appears to be a much harder scoping boundary
then I expected.  Or rather that class b is really class A::B
and as such has no knowledge of ancestory to A.

class A
   @a = "me"
   class B
     def t
       puts @a
     end
   end
end

A::B.new.t

this is suggested by this returning nil.

Charles Comstock