From: Robert Klemme <bob.news@...>
Date: 2004-12-04T00:32:41+09:00
Subject: Re: ordered hash ?


"David A. Black" <dblack@wobblini.net> schrieb im Newsbeitrag
news:Pine.LNX.4.44.0412030658240.26976-100000@wobblini...
> Hi --
>
> On Fri, 3 Dec 2004, Robert Klemme wrote:
>
> > >  I guess I'd prefer to see hash order be a
> > > characteristic of every hash (without an exception raised),
regardless
> >
> > Please, not of every Hash - just the OrderedHashes.  IMHO space and
time
> > overheads are significant enough to not include this into every hash.
>
> Right, just to the extent that a Hash is Ordered in the first place.
> (I had the feeling Matz was considering having all of them be ordered,
> but that may be wrong and/or a different matter.)

Hm, might be.  I can't remember such a statement but then again - I don't
read every single posting.  So this might have slipped through my fingers.
Still I don't think it's a good idea to make all hashes insertion ordered.

I could imagine a solution that uses a callback instance for greatest
flexibility.  That way even insertion order could be easily realized:


class OrderedHash
  include Enumerable

  # callbacks for various events
  class InstanceCallbacks
    def hash_instance(o) o.hash end
    def insert(key,val) end
    def update(key,val) end
    def remove(key,val) end
    def compare(a,b) a<=>b end
  end

  class InsertionOrderCB < InstanceCallbacks
    def initialize() @ins = [] end

    def insert(key,val) @ins << key end
    def remove(key,val) @ins.delete key end

    def compare(a,b)
      return 0 if a <=> == 0

      @ins.each do |x|
        if a <=> x == 0
          return -1
        elsif b <=> x == 0
          return 1
        end
      end

      raise "Internal Error"
    end
  end

  def initialize(ih = InsertionOrderCB.new,&b)
    @ih = ih
    # ...
  end

  def store(key,val)
    # use @ih instance handler to determine order...
  end

  def delete(key)
    # ...
  end
end


Kind regards

    robert