From: Dave Burt <dave@...>
Date: 2005-08-03T10:21:05+09:00
Subject: Re: Module that keeps track of instance count?

<francisrammeloo@hotmail.com> wrote...
> Hi,
>
> I need some of my classes to keep track of their number of instances.
> To avoid duplication I thought it was a good idea to put this
> functionality in a separate module:
> <snip counting code>

Here's a different way to do it:

module InstanceCounter
  def instance_count(include_subclasses = true)
    count = 0
    GC.start  # <- this line is optional
    ObjectSpace.each_object do |obj|
      count += 1 if obj.class == self || include_subclasses && 
obj.kind_of?(self)
    end
    count
  end
end

class Foo
  extend InstanceCounter
end

class Bar < Foo
end

Foo.instance_count  #=> 0
Bar.instance_count  #=> 0
a = [Foo.new, Bar.new, Bar.new]
Foo.instance_count  #=> 3
Foo.instance_count(false)  #=> 1
Bar.instance_count  #=> 2

Cheers,
Dave