From: Vasco Andrade e Silva <vascoas@...>
Date: 2007-11-16T02:38:46+09:00
Subject: Re: Shadowing bug??

Robert Klemme wrote:
> 2007/11/14, Vasco Andrade e Silva <vascoas@gmail.com>:
>> >
>> 1
>>
>> > f_ko({:xpto => "ohoh"})
>> :in_lambda
>> "ohoh"
>> {:xpto=>"ohoh"}
>> "ohoh"
>> {:xpto=>"ohoh"} # :-)
> 
> Just let me add that even though this is fixed IMHO it is a bad idea
> to use the same identifier in both cases if you want to keep them
> separate.  This can likely cause confusion.

I don't agreed with you. Shadowing, IMHO, is a very useful (and 
powerful) way to express semantic and execute "best practices".

Example:
Imagine you want to process a tree (as i wanted). Suppose that in the 
process of that computation you call "defn_to_sexp". This method 
receives a node (tagged with :defn).
In this case i wanted to do a "special" process to the args branch of 
the tree. So, and because i didn't want to declare another function 
visible from class scope, i created a proc (process_args). This proc 
should receive the tree branch (i.e. "node") and other variable witch 
represents a computation over some other branch of defn's node.

Here goes a simple sample:
def defn_to_sexp(node)
  process_args = lambda do |n, has_block|
    ...
  end
  ...
  has_block = process(...)
  process_args.call(args_node(node), hash_block)
  ...
end

i have more semantic if i can call the word "node" instead of the word 
"n" in lambda's arg: I want to shadow the node variable.
This is a case, IMHO, where it's a good idea "to use the same identifier 
in both cases".

In this case i would wanted to write:
def defn_to_sexp(node)
  process_args = lambda do |node, has_block|
    ... # i don't want to access to the outer node
        # and "node" says more than "n"
  end
  ...
  has_block = process(...)
  process_args.call(args_node(node), hash_block)
  ...
end


Regards,
Vasco Andrade e Silva
-- 
Posted via http://www.ruby-forum.com/.