From: Ruby Newbee <rubynewbee@...>
Date: 2009-12-14T18:58:04+09:00
Subject: about class and module

Hello,

Coz Ruby's class and module are close to Perl's, I think it's not hard
to understand for them.
I wrote a note below for learning them, if I'm not correct, please
point it out, thanks.


1. class is defined with the keyword of "class", module is defined
with the keyword of "module".

for example, define a class:

class Myclass
   def echo (a,b)
       puts a + b
   end
end

define a module:

module Mymod
   def echo (a,b)
       puts a+b
   end
end


2. If we want to call the methods in a class, need to instantiate the
class with "new" (except the class method).
    If we want to call the methods in a module, need to include it
(except the module method).

call the methods in a class:

class Myclass
   def echo (a,b)
       puts a + b
   end
end

x = Myclass.new
x.echo("hello","world")

call the methods in a module:

module Mymod
   def echo (a,b)
       puts a+b
   end
end

include Mymod
echo "hello","world"


3. class itself has class method, module itself has module method.
    if we call a class method or a module method, won't use "new" or "include".

the class method:

class Myclass
   def Myclass.echo(a)
       puts a
   end
end

Myclass.echo("hello world")

the module method:

class Mymod
   def Mymod.echo(a)
       puts a
   end
end

Mymod.echo "hello world"


4. the calling and called relationship between class and module:

A module can contain methods, constants, other modules, and even classes.
A module can inherit from another module, but it may not inherit from a class.
As a class may include a module, it may also include modules that have
inherited other modules.