Ruby class instance variables and inheritance

Question

I have a Ruby class called LibraryItem. I want to associate with every instance of this class an array of attributes. This array is long and looks something lik

Answer 1

In LibraryBook variable @attributes is a new independent variable, instance variable of object LibraryBook, so its not initialized and you get error "undefined method ... for nil"
You should to initialize it by LibraryItem attribut's list before using

class LibraryBook < LibraryItem
  @attributes = LibraryItem::attributes + ['ISBN', 'pages']
end