From: Rick DeNatale <rick.denatale@...>
Date: 2006-10-18T08:07:20+09:00
Subject: Re: include inside and outside classes

On 10/16/06, Pit Capitain <pit@capitain.de> wrote:
> John Ky schrieb:
> > Why is it that when I can do this:
> >
> >> include Math
> >> puts sqrt(169)
> >
> > I can't do this?:
> >
> >> class X
> >>   include Math
> >>   puts sqrt(169)
> >> end
>
> Rick has already written about the differences between class scope and
> toplevel scope. (Are you reading this, Tom?)
>
> With #include you can call the Math methods in instance methods:
>
>    class X
>      include Math
>      def m
>        puts sqrt(169)
>      end
>    end
>
>    X.new.m  # => 13.0

And the reason that this works is that these functions are module
functions which act like a combination of class methods for the
module, and private instance methods.

The first lets you say

Math.sqrt(4)

and the second lets you say

class A
   include Math
   def meth
       sqrt(4)
   end
end

And the way you make a module function in one of your own modules is
either like this:

module MyModule

   def foo
   end

   module_function :foo
end

or

module MyModule

   module_function
   def foo
   end
end

The module_function method works like private and protected. With
arguments it makes specific methods module_functions, without
arguments it makes subsequently defined methods module_functions.


-- 
Rick DeNatale

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