From: Robert Dober <robert.dober@...>
Date: 2008-07-23T05:08:19+09:00
Subject: Re: simple module for "count my instances" behaviour

On Tue, Jul 22, 2008 at 8:07 PM, ara.t.howard <ara.t.howard@gmail.com> wrote:

Maybe there is a way to leave Class alone ;)

This will track instances for all ancestors of InstanceTracker.

module InstanceTracker
  # Define a block that defines the included
  inclusion = proc { | by_module |
    singleton = class << by_module; self end

    unless Class === by_module then
      singleton.send :define_method, :included, &inclusion
      return
    end

    by_module.instance_variable_set "@__instances__", []
    singleton.send :define_method, :inherited, &inclusion
    singleton.module_eval do
      def new *args, &blk
        o = allocate
        o.send( :initialize, *args, &blk )
        @__instances__ << o
        o
      end
      def instances; @__instances__ end
    end
  }
  # Define included in base module
  class << self; self end.
    send :define_method, :included, &inclusion
end # module InstanceTracker


M2 = Module::new {
  include InstanceTracker
}
class A
  include M2
end
B = Class::new A do
  def initialize; 42 end
end

A::new
B::new
A::new
p A.instances
p B.instance

----------------------------------

One could take special care of classes that define a custom new, but
that would make the code too complicated for the demonstrational
purpose I feel.

HTH
Robert

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--
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