From: Marcin Raczkowski <mailing.mr@...>
Date: 2007-11-14T05:21:42+09:00
Subject: Re: Shadowing bug??

Vasco Andrade e Silva wrote:
> Hi,
> 
> def f_ok(node)
>   func = lambda {|n| p(:in_lambda, n); n }
>   p node, func.call(node[:xpto]), node
> end
> 
>> f_ok({:xpto => "ohoh"})
> :in_lambda
> "ohoh"
> {:xpto=>"ohoh"}
> "ohoh"
> {:xpto=>"ohoh"}
> 
> def f_ko(node)
>   func = lambda {|node| p(:in_lambda, node); node }
>   p node, func.call(node[:xpto]), node
> end
> 
>> f_ko({:xpto => "ohoh"})
> :in_lambda
> "ohoh"
> {:xpto=>"ohoh"}
> "ohoh"
> "ohoh" # ohoh... should be {:xpto=>"ohoh"}, or not??
> 
> I can't get any kind of explanation for this. Does anybody have one?
> Why "node" in lambda isn't shadowed correctly (as i expected, at least)?
> Well "node" is shadowed correctly but seems to be producing side
> effects...
> 
> Thanks,
> Vasco Andrade e Silva

I remember someone mentioned that it's possible to do some strange 
things in lambda (modyfing variable passed beeing one of them), but 
there's nothing in this funcition or lambda that would modify "node", i 
think there might be a scope problem that makes node variable in 
function beeing overvriten when part of node is in lambda


irb(main):014:0> def f_ko(node)
irb(main):015:1>   func = lambda {|node| p(:in_lambda, node); node }
irb(main):016:1>   p node, func.call("bleh"), node
irb(main):017:1> end
=> nil
irb(main):018:0> f_ko({:xpto => "ohoh"})
:in_lambda
"bleh"
{:xpto=>"ohoh"}
"bleh"
"bleh"
=> nil


this seems to confirm that using |node| will overwrite node in function, 
i'm not sure if it's intended scope behaviour tho