From: ptkwt@...1.aracnet.com (Phil Tomson)
Date: 2003-01-22T18:00:03+09:00
Subject: Re: accessors for module instance vars

In article <Pine.LNX.4.33.0301220531480.26588-100000@eli.fsl.noaa.gov>,
ahoward  <ahoward@fsl.noaa.gov> wrote:
>On 22 Jan 2003, Phil Tomson wrote:
>
>> That's certianly one way to do it...  I guess I'm looking at Evolvable as
>> more of a namespace than a class that defines an object, though.
>
>a singleton is really nothing more than an encapsulation of some data and some
>methods - just like a namespace - but i understand your objection
>
>> And if I leave it as a module it could be mixed into a class later (though
>> that's not how I'm using it now) and all of the 'module instance variables'
>> would also end up in the class it was mixed into....
>
>i don't think it works that way :
>
>  module M
>    attr_accessor :x
>    @x = 42
>  end
>
>  class Foo; include M; end
>
>  p Foo.new.x  # >> nil
>
>the instance variable STAY in M, that's what i was referring to when i said i
>was unsure of the semantics.

this works:

 module M
  def x
     if not defined? @x
       @x = 0
     end
     @x
   end

   def x=(x)
     @x=x
   end
 end

 class Foo; include M; end

 Foo.new.x #-> 0

However, those are instance methods (x and x=) defined in module M and 
since M can't be instantiated they are only callable after M is mixed into 
a class and an instance of that class is created.

I wonder if there is a way to mixin module methods so that they become 
instance methods of a class?

module M
  def M.x
    if not defined? @x
      @x=0
    end
    @x
  end
end

class MyM
  include_module_methods_of M #somehow
end

MyM.new.x #-> 0

Anyone know of a way to do this?  (I have no pressing need for this, just 
curious)

Phil

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