str = "a string"              # we assign str a new object
  wr = WeakRef.new(str)  # Then create a weak reference to the same object. 
 
  str = nil  # There are no longer any references to our object.
               # So the garbage collector is now free to take it at any time even with a weak reference left.
 
  ### Now we order the garbage collector to work immediately.
  ObjectSpace.garbage_collect
  if wr.weakref_alive?
    # This test tells us wr is valid
  else
    # Weak reference is indeed no longer valid.
  end
 

 
require 'weakref'
class Player
  ### define some accessors
  def follower=(f)
    @follower = WeakRef.new(f)
  end
 
  def follower
    return false if @follower == nil
 
    if @follower.weakref_alive?
      @follower
    else
      false
    end
  end
end
 
### create 2 players
p = Player.new
p2 = Player.new
 
### p2 referenced as the follower of p1
p.follower = p2
 
### p2 is no longer valid
p2 = nil
ObjectSpace.garbage_collect
 
### p.follower returns false instead of the follower.
puts p.follower