From: raja@... (Raja S.)
Date: 2001-03-07T00:40:03+09:00
Subject: [ruby-talk:12143] Re: disassembling and reassembling a hash

ts <decoux@moulon.inra.fr> writes:

>R>   keys,values = h.keys, h.values    # disassemble
>R>   new_vals = norm_v (values)        # normalize
>R>   Hash.make (keys, new_vals)        # reassemble

>     h1 = {}
>     h.each { |k, v| h1[k] = norm_v(v) }

>   no ?

Not quite.  v[i][j] is normalized based on -all- the values in v not just
those in v[i].  Hence in the above norm_v (values) takes a vector of vectors
formed from the values of the hash.

>>> p.s. is there a way to override a class method like Hash.new -without-
>>> sub-classing?  It appears that class methods can't be aliased hence
>>> redefinition of something like Hash.new doesn't seem possible? 


>   class Hash
>      class << self
    ...

Aha!  'self' now refers to the class 'Hash' and by creating an anonymous
super-class for it, class methods of 'Hash' become its instance methods and
hence can be aliased.  I didn't want to go "downwards" in terms of creating
a sub-class of Hash but didn't occur to me that one could go "upwards" and
create an anonymous super-class!  Very nice and very clever!  Thank you.

The brilliance of matz comes thru again in his design choices and how
harmoniously the concepts of Ruby hang together!

Now I've got:

class Hash
  class << self
    alias :old_new :new
    def new (*args)
      if ((args.length==2) && (args[0].type==Array) && (args[1].type==Array)
#	  && (args[0].length == args[1].length)
#     if more keys pad with nil; if more values, ignore
	  )
	h={}
	keys, vals = *args
	keys.each_with_index { |k, i|
	  h[k] = vals[i]
	}
	return h
      else
	old_new (*args)
      end
    end
  end
end

Question: since we have #to_a, #keys, #values --- all used to disassemble a
          hash would it be useful to enhance Hash.new(key,values) in the
          core to assemble a hash from an array of keys and values?
          Shouldn't break anything existing (I think).

Question: my original question on the order of the entries returned by #keys
          and #values remains.  

Raja