From: Kris <iamkris@...>
Date: 2005-11-29T07:37:29+09:00
Subject: Question on class-declarations

Yet Another Ruby Nuby (YARN) question.

I see Rails makes extensive use of class-declarations.

For example:

class LineItem < ActiveRecord::Base
  belongs_to :product
......

belongs_to is a class-declaration in the above code. Coming from a C
family of languages I could not grasp this initially. When does this
code get executed - does it happen when the class is loaded for the
first time or every time a new instance of the class is created?

In this case I think the class-declaration code(belongs_to) looks at
the corresponding database table structure and injects attributes and
methods into the LineItem class. Am I right?

I created the following example

class B
 def hello
   print "Hello"
 end
end

class D < B
  hello
 def bye
   print "bye"
 end
end

I tried this in irb and got an error. Why doesn't this work? In Rails I
think mixins are used to provide this kind of functionality.

To me these seem to be idioms of the language. Is there a site where
you could find gems like these?

Thanks.