Ruby's mixin is quite slick. But I was confused by include and extend for a while until I stumble upon this posting Extending your include knowledge of Ruby. 

Both include and extend are used for mixing-in module methods. "extend" adds methods from a module into a class as class methods. "include" adds methods from a module into a class as instance methods.

Do not attempt to include or extend another Class. Say, you have:

In my Rails application direcotory, when I run "rdoc", I got an error message:

Directory doc already exists, but it looks like it
isn't an RDoc directory. Because RDoc doesn't want to risk
destroying any of your existing files, you'll need to
specify a different output directory name (using the
--op <dir> option).

That's because rails generated "doc" directory that rdoc don't like. To fix this, we can either use rake:

$ rake doc:app

Or specify another directory name to rdoc:

$rdoc --op rdoc_dir

Install RoR 2.0

At this date, Ruby on Rails 2.0 is the latest greatest RoR, which is not available in Portage yet.

Ruby language

If you want to install the ruby from source, then download the source from http://www.ruby-lang.org/en/downloads/.

Or, you can use emerge:

# emerge -pv  dev-lang/ruby