From: Austin Ziegler <austin@...>
Date: 2004-04-25T10:01:37+09:00
Subject: Re: IdentityHash, like Hash but with keys using equals? vs eql?

On Thu, 8 Apr 2004 14:00:26 +0900, Jean-Hugues ROBERT wrote:
> At 07:44 08/04/2004 +0900, you wrote:
>> Jean-Hugues ROBERT <jean_hugues_robert@yahoo.com> writes:
>>> BTW: I need that to detect "true" circular paths when walking a
>>> tree/graph. Rigth now I detect false circulars when nodes' values
>>> compare equal where in fact it is two different node objects (with
>>> the same "value").
>> Can you just hash the ids?
>> hash[obj.id] = blah
> Yes !
> So: an IdentityHash in ruby is just a Hash, but
> with obj.object_id() in it vs the obj itself.
> Makes a lot of sense.
> Thanks George !
>
> Jean-Hugues
> PS: As one said, in Computer Science everything is solvable by adding one
> indirection level.

class IdentityHash < Hash
  def [](k)
    super k.object_id
  end

  def []=(k, v)
    super k.object_id, v
  end
end

Note that this will, of necessity, prevent this from doing anything 
meaningful:

  i = IdentityHash.new
  i["abc"] = "def"
  puts i["abc"] # => nil

-austin
--
austin ziegler    * austin@halostatue.ca * Toronto, ON, Canada
software designer * pragmatic programmer * 2004.04.24
                                         * 20.57.28