From: Gavin Sinclair <gsinclair@...>
Date: 2003-01-23T02:59:31+09:00
Subject: Re: extend (Re: a single class that supports multiple facets/interfaces)

On Thursday, January 23, 2003, 4:12:58 AM, Gavin wrote:

>> Well, here's some cool code then:

> ... and some more:

... and finally (I just noticed this in fileutils.rb)

Ever find it annoying when you create a module which is basically
intended to be a namespace/container for a set of functions, and they
don't work because you have to use "public_module_method" or whatever?

Here's another way.

   module M
     def hi
       "hi"
     end
   end

   M.extend M           # These

   module M             # three are
     extend M
   end

   module M             # equivalent
     extend self
   end

   M.hi                 # => "hi"


The code I saw opted for "extend self" after all the methods had been
defined.  This had me scratching my head wondering what it meant.  A
comment up the top switched the light on.  But it could have been
written "extend FileUtils", which would have been a bit clearer, and
it could have been done up the top, with a comment saying all methods
are hearby public module methods.

That's right, it could be up the top.  Check this:

   >> module M
   >>   def hi
   >>     "hi"
   >>   end
   >>   extend M
   >>   def lo
   >>     "lo"
   >>   end
   >> end
   => nil
   
   >> M.hi
   => "hi"
   
   >> M.lo
   => "lo"

Apparently, using "extend" merely hooks something up behind the
scenes, rather than dumping a lot of information into the target
module.  This is not particularly surprising, but it's still nice to
have a language that lets you play around like this and experiment.

Gavin