From: Eero Saynatkari <eero.saynatkari@...>
Date: 2006-08-14T00:49:41+09:00
Subject: Re: Modules -> do I have is straight?

Carl Jenkins wrote:
> I was hoping I could expand on the thread a little bit...
> 
> I sort of understand modules, according to what I have read in my fancy 
> ruby book and this forum modules are like superclasses. But, what about 
> this < ?
> Doesn't this allow a class to "become" a subclass of another by way of 
> inheritance. Not sure I am catching the difference between the two.

Modules should really not be used like superclasses--although
you are correct, an #included module does become an ancestor
of the #including class and method lookup follows this. The
commonly used name for the module behaviour is 'mixin'.

I personally prefer modules for mainly two cases:

1) 'Intersecting' behaviour, something that is added to multiple
   classes as an enhancement but does not really make the classes
   'related' enough for an inheritance relationship.

2) Variable composition--a class can be customised/enabled/disabled
   for certain tasks by adding/withholding/changing its module
   composition. This can, of course, also be achieved by either
   actual composition by variables or then by subclassing.

> Also, I am not quite sure I understand how namespaces works in ruby.
> In java you create a package ( i know you all know this already I am 
> just saying it for my benefit) to place related classes in. Say for 
> example com.jenkins.util.MyFancyClass. If I want to use this class in 
> another package com.jenkins.library any classs in library would just 
> import it. How does this work in ruby?
> Most of the code I have seen is in the same class or at least the same 
> direcctory. Is it typical for ruby applications to create a package 
> structure similar to a java app?

The namespace, unlike in Java, is in no way enforced and it
cannot be used to resolve a file's location in the filesystem.
It is strictly a convenience to give the code some structure
and to insulate it from namespace clashes.

It is certainly possible to put your code in a similar namespace
to what you would use in Java:

  module Com
    module Company
      module ProjectName
        module LibraryName
          class SomeClass
            # ...
          end
        end
      end
    end
  end

Typically, though, only the ProjectName/LibraryName downwards
is used.

I think the most common  file layout is the one required by
install.rb/setup.rb (see http://raa.ruby-lang.org) or, more
recently, RubyGems.

> Thanks for your time!


-- 
Posted via http://www.ruby-forum.com/.