Ruby class instance variables and inheritance
- by rlandster
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 like
['title', 'authors', 'location', ...]
Note that these attributes are not really supposed to be methods, just a list of attributes that a LibraryItem has.
Next, I want to make a subclass of LibraryItem called LibraryBook that has an array of attributes that includes all the attributes of LibraryItem but will also include many more.
Eventually I will want several subclasses of LibraryItem each with their own version of the array @attributes but each adding on to LibraryItem's @attributes (e.g., LibraryBook, LibraryDVD, LibraryMap, etc.).
So, here is my attempt:
class LibraryItem < Object
class << self; attr_accessor :attributes; end
@attributes = ['title', 'authors', 'location',]
end
class LibraryBook < LibraryItem
@attributes.push('ISBN', 'pages']
end
This does not work. I get the error
undefined method `push' for nil:NilClass
