From: Stefan Lang <perfectly.normal.hacker@...>
Date: 2008-01-25T20:42:46+09:00
Subject: Re: What this code means?

2008/1/25, MohsinHijazee <mohsinhijazee@gmail.com>:
> Hello!

Hello!

>    I am new to Ruby, can anyone explain what this code snippet is
> trying to do?

First you have to understand the following Ruby construct:

  class << some_object
    def hello
      puts "hello"
    end
  end

The "class << some_object" line opens the "eigenclass"
of some_object. The eigenclass is Class object that
belongs solely to some_object and thus we're not
interfering with any other objects class. All methods
added in "class << some_object" belong only
to some_object.

  some_object.hello # prints "hello"

Now to your example:

  module YourLastModule

        # At this point, self refers to YourLastModule

        # Thus here we are opening the eigenclass
        # of YourLastModule.
        class << self

           # This method is defined on the YourLastModule
           # object (and _not_ on instances of YourLastModule).
           #
           # The included method of a module is called by
           # Ruby when the module is included in a class
           # or another module. The argument c is the including
           # class or module.
           def included(c)

              # Here we open up the eigenclass of the including
              # class.
              class << c

                # Adding a method to the including class object
                # (the method is _not_ available to instances of the class).
                def say_hello(name)
                   return "Hello, " + name
                end

              end
           end
        end
  end

In effect, the example demonstrates how to add
class methods to including classes.

  class Foo
    include YourLastModule
  end

  Foo.say_hello("Arthur") # => "Hello, Arthur"

I'd say this stuff belongs into the advanced section
of ruby learning material.

HTH,
  Stefan