From: Matthew D Moss <matthew.moss@...>
Date: 2005-09-12T08:06:32+09:00
Subject: Misunderstanding of instance variables

I'm learning Rails, and trying to setup image upload in a form. As part
of that, my image model looks something like this:

   class Image < ActiveRecord::Base
      validates_presence_of :content_type
      validates_format_of :content_type, :with => /^image/, :message =>
"must be an image"

      def image_file=(arg)
         self.content_type = arg.content_type.chomp
      end
   end


Okay, so the above basically works. But I wondered why the author I
borrowed this from used "self." instead of @ -- I thought both would
essentially reference an instance variable.

So I replaced the one line to look like this:

         @content_type = arg.content_type.chomp

and it fails, triggering my validation checks.

What gives?