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I didn't see a final answer to the original post. I recently read the book "Eloquent Ruby" by Russ Olsen, so decided to add my take-away here. The scope in which the first example defines the single-@ variable is a class-scope, i.e., if the keyword self were to appear outside a method def but still within the class definition, it would reference the object Document, which is in turn an instance of the Class class. The first example therefore defines a class instance variable, i.e., the variable @default_font is an instance variable of the object Document, a class object. This class instance variable should only be accessed via the class level accessor methods, e.g., Document.default_font, rather than say, an_instance_of_Document.default_font So if you define the attr_accessors: <pre><code>class Document @default_font = :Arial # this is a class instance variable, # def self.default_font # @default_font # end # # def self.default_font=(font) # @default_font = font # end # or replace the above two class methods with the following class << self attr_accessor :default_font end end </code></pre> Here's some irb output: <pre><code>1.9.3p429 :002 > require './document.rb' => true 1.9.3p429 :004 > Document.default_font => :Arial 1.9.3p429 :005 > Document.default_font = :Times => :Times 1.9.3p429 :006 > Document.default_font => :Times 1.9.3p429 :007 > doc = Document.new => #<Document:0x007fe6730d8228> 1.9.3p429 :008 > doc.default_font NoMethodError: undefined method `default_font' for #<Document:0x007fe6730d8228> </code></pre> The fact that the second example in the original post does not contain a single-@ variable definition outside a method def, indicates that the @default_font here is an instance variable, which can only be referenced by an instantiated object of class Document. <pre><code>class Document def default_font=(font) @default_font = font # this defines and set an instance variable end def default_font @default_font # this defines an instance variable end # or above two defs can be replaced by the following attr_accessor :default_font # this defines the instance variable and access methods end </code></pre> Here's some irb output: <pre><code>1.9.3p429 :001 > require './document.rb' => true 1.9.3p429 :002 > Document.default_font NoMethodError: undefined method `default_font' for Document:Class 1.9.3p429 :003 > doc = Document.new => #<Document:0x007ffbf1136f88> 1.9.3p429 :004 > doc.default_font => nil 1.9.3p429 :005 > doc.default_font = :Arial => :Arial 1.9.3p429 :006 > doc.default_font => :Arial </code></pre>
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