From: Brian Candler <b.candler@...>
Date: 2008-11-17T21:38:35+09:00
Subject: Re: How does Ruby handle namespace?

I'd say it's probably quicker to read the Ruby documentation on these 
topics, rather than asking how Java is different, because Java *is* 
different.

A good start is http://www.ruby-doc.org/docs/ProgrammingRuby/ - this is 
the free, 1st edition of the "Pickaxe" Programming Ruby book, written 
for ruby 1.6.

There is now a revised 2nd edition for 1.8, and the 3rd edition for 1.9 
is in beta. These are available from bookshops or www.pragprog.com (in 
PDF, book, or combo pack)

The 1.6 stuff is pretty much still valid, it's just that 1.8 adds new 
classes and methods.

> In Java, it uses import to include other classes from other packages. In
> ruby, I only found that require statement can do this. When the ruby
> scripts are located in different directories, I have to use the "../../"
> to indicate these dependency directories. Is there a standard or better
> way to declares package? Does ruby have something like CLASSPATH in
> Java?

In brief:

"require 'foo'" looks for file foo.rb, and loads and runs it (unless 
foo.rb has already been loaded, in which case it's a no-op)

The search path is the array $LOAD_PATH (or $: for short), and the 
record of which files have already been loaded is in $LOADED_FEATURES

Namespaces are handled entirely separately, using class and module 
keywords. A Module defines a new namespace, and a Class is a Module 
which can be instantiated to create objects.

How you organise your files is up to you, but it is conventional to have 
a lib/ subdirectory for your project. Then

module Foo
  class Bar
    ...
  end
end

would typically be put into lib/foo/bar.rb

If you do this, then you can load it using

  require 'foo/bar'
  obj = Foo::Bar.new

All this requires is lib/ to be in your search path.

You can arrange this from the command line:

   ruby -Ilib main.rb

or you can do something like this in your main program:

   $LOAD_PATH.unshift(File.dirname(__FILE__)+"/lib")

If your main program is inside a bin/ directory then you'd do

   $LOAD_PATH.unshift(File.dirname(__FILE__)+"/../lib")

HTH,

Brian.
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