From: Samuel Tesla <samuel@...>
Date: 2003-12-06T13:02:07+09:00
Subject: Re: WeakRef and Object#hash

"Robert Klemme" <bob.news@gmx.net> writes:
>
> Then you need to sub class Hash and override some methods if you want the
> WeakHash to look like a normal hash from the outside.

Indeed, with the exception of the problem I posted about the class no
longer being a a weak reference, here's that subclass.  Works out
fairly well:

## test.rb

require 'weakref'

class WeakKey < WeakRef        
  def initialize(aRef)
    super(aRef)

    # We need to change #eql? on the incoming object because the
    # method defined in object.c does not actualy check
    # #object_id it actually compares the VALUE structs passed
    # in.  So when I override #object_id below, it doesn't completely
    # take care of the problem.

    class << aRef
      def eql?(ref)
        begin
          self.object_id == ref.object_id
        rescue WeakRef::RefError
          false
        end
      end
    end
  end

  # We need to override this so that anything that asks for our ID
  # will actually receive the ID of the object we are pretending to be.

  def object_id
    begin
      __getobj__.object_id
    rescue WeakRef::RefError
      0
    end
  end

  # Object#id is deprecated, but people use it still.  Let's make sure
  # they get the proper ID when they do.

  alias_method :id, :object_id

  # From Robert Klemme.  This simply calls the hash function from the
  # actual object.

  def hash
    begin
      __getobj__.hash
    rescue WeakRef::RefError
      0
    end
  end

  # Also from Robert Klemme.  Same idea as #hash.  

  def eql?(ref)
    begin
      __getobj__.object_id == ref.object_id
    rescue WeakRef::RefError
      false
    end
  end
end

a = Object.new
b = WeakKey.new(a)
puts(a.eql?(b).to_s) # => true
puts(b.eql?(a).to_s) # => true