gistfile1.rb

class Foo
  def self.set_finalizer(obj)
    ObjectSpace.define_finalizer(obj,method(:finalize))
  end

  def self.set_finalizer2(obj)
    ObjectSpace.define_finalizer(obj,finalize2)
  end

  def self.finalize
   puts "finalizer"
  end

  def self.finalize2
    proc{ puts "finalizer 2" }
  end
end


Foo.set_finalizer(Foo.new)
Foo.set_finalizer2(Foo.new)