From: Robert Klemme <bob.news@...>
Date: 2004-04-14T17:14:16+09:00
Subject: Re: New Local Variable Scope rule


"Shashank Date" <sdate@everestkc.net> schrieb im Newsbeitrag
news:c5id4r$22o3g$1@ID-194283.news.uni-berlin.de...
> In one of Matz's slides at RubyConf ,
>
> (http://www.rubyist.net/~matz/slides/rc2003/mgp00012.html)
>
> he mentions his New Local Variable Scope rule as follows:
>
> #---------------------------------------------------------------
> def foo
>     a = nil
>     ary.each do |b|
>         # b is block local
>         c = b
>         a = b
>         # a and c are local to the method
>     end
>     # a and c available here
> end
> #---------------------------------------------------------------
>
> I was wondering what would happen if it was written as follows:
>
> #---------------------------------------------------------------
> def foo(&block)
>     a=nil;
>     ary.each(&block)
> end;
>
> foo(lambda {|b| a=b; c=b})
> #---------------------------------------------------------------

First of all both examples are erroneous IMHO because ary is not defined
in foo().

> In other words, in general, what is the advantage of having variables in
> closures leak out?

Your second example will not modify the a defined in foo() because the
binding takes place at the point of invocation, i.e. another scope.  If
you do

def foo(&block)
    a=nil;
    ary.each(&block)
    puts "a=#{a.inspect}"
end;

foo(lambda {|b| a=b; c=b})
puts "a*#{a.inspect}"

You'll see
a=nil
a*<last enum element>

Regards

    robert