From: Eero Saynatkari <eero.saynatkari@...>
Date: 2006-08-11T07:27:04+09:00
Subject: Re: Modules -> do I have is straight?

Simon Harrison wrote:
> A related question: is this why many libraries nest classes inside a
> main module?
> 
> i.e.
> 
> module DataBase
>   class Table
>     class Column
>       ...
>     end
> 
>    class Row
>      ...
>    end
>  end
> end
> 
> Are their any good explanations of designing programs using this
> convention?

This is apart from modules' normal usage as mixins.

The module is just there to provide a structure or a
namespace for the code, similar to Java's packages.

When a programmer #requires your file, they must refer
to your class as DataBase::Table which is useful for all
the normal reasons.

One interesting thing arising from modules in fact being
Modules and the top-level execution context being an Object
is that you can reduce namespaces. In the event that a
programmer does not want to use your DataBase namespace
everywhere, they can #include it just like any other
Module and thereby mixing in its contents with normal
mixin semantics:

 module Foo
   Class Bar
   end
 end

 Bar.new       # Error
 Foo::Bar.new  # OK

 include Bar

 Bar.new       # Now OK also!

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