From: James Gray <james@...>
Date: 2009-08-07T03:53:22+09:00
Subject: Re: Kernel's module methods?

On Aug 6, 2009, at 11:32 AM, Joel VanderWerf wrote:

> James Gray wrote:
>> Yes, and I generally prefer extend(self) to module_function after  
>> much time trying it both ways.  Unfortunately, I always seem to  
>> eventually run into issues after using module_function, say with  
>> constant resolution or included modules (like you mentioned).
>
> Can you post an example of the constant resolution problem next time  
> you come across it? I'm curious because I'm in the habit of using  
> module_function rather than extend(self), not for any good reason  
> except that it is perhaps more self documenting.

Here's an example I remember from just the other day (though it  
probably falls more under the included module problem).  Consider this  
simple module:

module MoreMath
   extend  Math  # needed for self::sqrt
   include Math  # needed for self#sqrt and PI

   module_function

   def circ(r)
     2 * PI * r
   end

   def dist(x1, y1, x2, y2)
     sqrt((x2 - x1) ** 2 + (y2 - y1) ** 2)
   end
end

p MoreMath.circ(12)
p MoreMath.dist(0, 0, 3, 4)

Note that I need both an extend and include to get just that much to  
work.  Or, I can just do:

module MoreMath
   include Math
   extend  self

   def circ(r)
     2 * PI * r
   end

   def dist(x1, y1, x2, y2)
     sqrt((x2 - x1) ** 2 + (y2 - y1) ** 2)
   end
end

p MoreMath.circ(12)
p MoreMath.dist(0, 0, 3, 4)

Anyway, I too like module_function() and have used it a lot.  I like  
how it makes the instance methods private so they don't add to an  
object's public interface when mixed in.

It just seems like I have more control with extend(self) so I tend to  
reach for that now.

James Edward Gray II