From: matz@... (Yukihiro Matsumoto)
Date: 1997-12-15T17:07:22+09:00
Subject: [ruby-dev:1094] Re: [Req] object refference

まつもと ゆきひろです

In message "[ruby-dev:1091] Re: [Req] object refference"
    on 97/12/15, Yukihiro Matsumoto <matz@netlab.co.jp> writes:

|まつもと ゆきひろです

|finalizerを使えばできますね．ということはRubyレベルで書ける？

とりあえず以下のようなのはいかがでしょう．
委譲用のクラスDelegaterを使ってます．

-- weakref.rb
# Weak Reference class that does not bother GCing.
#
# Usage:
#   foo = Object.new
#   foo = WeakRef.new(foo)
#   ...
#   ObjectSpace.garbage_collect
#   ...
#   foo.hash # => Raises WeakRef::RefError (because original GC'ed)

require "delegate"

class WeakRef<Delegater

  Exception :RefError

  ID_MAP =  {}
  ID_REV_MAP =  {}
  ObjectSpace.add_finalizer(lambda{|id|
			      rid = ID_MAP[id]
			      if rid
				ID_REV_MAP[rid] = nil
				ID_MAP[id] = nil
			      end
			      rid = ID_REV_MAP[id]
			      if rid
				ID_REV_MAP[id] = nil
				ID_MAP[rid] = nil
			      end
			    })
			    
  def initialize(orig)
    @id = orig.id
    ObjectSpace.call_finalizer orig
    ID_MAP[@id] = self.id
    ID_REV_MAP[self.id] = @id
  end

  def __getobj__
    unless ID_MAP[@id]
      $@ = caller(1)
      $! = RefError.new("Illegal Reference - probably recycled")
      raise
    end

    ObjectSpace.each_object do |obj|
      return obj if obj.id == @id
    end
  end

  def alive?
    if ID_MAP[@id]
      true
    else
      false
    end
  end

  def []
    __getobj__
  end
end

-- delegate.rb
# Delegation class that delegates even methods defined for Object class.
#   which can not covered with normal method_missing hack.
#
# Usage:
#   foo = Object.new
#   foo = Delegater.new(foo)
#   foo.type # => Object

class Delegater

  def initialize(obj)
    @obj = obj
  end

  def __getobj__
    @obj
  end

  def method_missing(mid, *args)
    __getobj__.send mid, *args
  end

  DELEGATING_METHODS = [
    "nil?", "==", "===", "=~", "eql?", "hash", "type",
    "clone", "dup", "to_a", "to_s", "inspect", "methods",
    "singleton_methods", "private_methods", "instance_variables",
    "remove_instance_variable", "instance_of?", "kind_of?", "is_a?" ]

  for method in DELEGATING_METHODS
    eval "def #{method}(*args); __getobj__.send :#{method}, *args; end"
  end

end