Question

I feel this is fundamental to my understanding of Ruby and object-oriented programming in general, so I’m asking this fairly simplistic question here at the risk of looking foolish. I’ve been toying around with irb. I’ve created my first ever class:

$ irb
ruby-1.9.2-p290 :001 > class Person
ruby-1.9.2-p290 :002?>   attr_accessor :firstname, :lastname, :gender
ruby-1.9.2-p290 :003?>   end
 => nil 
ruby-1.9.2-p290 :004 > person_instance = Person.new
 => #<Person:0x007f9b7a9a0f70> 
ruby-1.9.2-p290 :005 > person_instance.firstname = "Bob"
 => "Bob" 
ruby-1.9.2-p290 :006 > person_instance.lastname = "Dylan"
 => "Dylan"
ruby-1.9.2-p290 :007 > person_instance.gender = "male"
 => "male"

So Person.new is my object, right? Or is my object the combination of class Person and the attributes I’ve defined for that class?

Answer 1

Your object is the result of running Person.new, which you’ve captured in person_instance.

In ruby, attributes don’t actually exist until they are first written, so before person_instance.firstname = "Bob", your instance has no attributes. After executing this statement it has a @firstname attribute, but no others.