From: "Florian Groß" <florgro@...>
Date: 2005-12-22T00:23:49+09:00
Subject: Re: Help with object scope

List Recv wrote:

> So,
> 1) How do I call C from class TestM without explicitly using its 
> namespace (M:C)?  Is there no way?  I don't want to modify Kernel or 
> anything, just have class C available.

Try this instead:

> class TestM
>   include M
>   def setup; C.blah; end
> end

A module is a set of instance methods and constants. It can either be 
used as a namespace or mix-in functionality. (For the latter you are 
collecting similar methods / constants together in one Module so you can 
add them to your own classes or objects easily.)

mod_or_cls.include(mod) will add all constants and instance methods of 
mod to mod_or_cls.

obj.extend(mod) will add all constants and instance methods of mod to an 
object itself.

Here's a sample:

module HalfString
   def half()
     self[0, length / 2]
   end
end

str = "foobar"
str.half() # raises NoMethodError
str.extend(HalfString)
str.half() # => "foo"

"hello".half() # raises NoMethodError

You can't ever include classes. You can only inherit from them.

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