From: Austin Ziegler <halostatue@...>
Date: 2005-02-19T11:48:41+09:00
Subject: Re: Module nesting and module vs. instance methods

On Sat, 19 Feb 2005 10:09:48 +0900, gga <GGarramuno@aol.com> wrote:
[...]
> I have a bunch of functions that, currently, have no particular
> class location. Currently, I am placing them in modules. As I have
> a bunch of them that are somewhat unrelated, I have been creating
> modules following the standard procedure I've used in other
> languages. That is, I'm using:
> 
> module MyCompany
>   module Module
>     def self.func1
>     end
>     def func2
>     end
>   end
> end


> Now... the problems I am facing are...
> 1) Ruby's name pollution on includes.
> 
> --- B ---
> module B
>   def bfunc
>     puts "bfunc"
>   end
> end
>
> --- A ---
> require 'B'
> 
> module A
+   include B
+
>   def afunc
>     puts "afunc"
>     bfunc
>   end
> end
>
> ---- some other code
> require "A"
> class X
+   include A
+
>   def initialize
>     afunc   # this should work
>     bfunc   # this should fail
>   end
> end

I presume that you mean the include statements I placed above.

> I want to have code that includes A, but does not include B.
> However, class X should not have access to functions in module B,
> which it never included.

This is not possible without doing some tricks. If you want A to
have access to B, but not allow X (which included A) to have access
to B, then you need to figure out some other way. Perhaps:

  module B
    def self.bfunc; end
  end

  module A
    def afunc; B.bfunc end
  end

  class X
    include A

    def xfunc; afunc; end
  end

But if A has included B, then when you include A, you'll get
everything that it knows about mixed into your class. This is the
fundamental capability of Ruby's mix-ins: the mix-in essentially
becomes a private part of the class into which it is mixed.

> 2) I also would like to have some modules that work either as
> include modules or as modules with stand-alone methods. Problem is
> that ruby will not "include" class methods.

try:

  module Shell
    def runcmd(command); ...; end
    module_functtion :runcmd
  end

  class Backup
    include Shell
  end

It does the same thing as you did, except nicer.

-austin
-- 
Austin Ziegler * halostatue@gmail.com
               * Alternate: austin@halostatue.ca