require 'pp'

class LibraryItem
  # class << self; attr_accessor :attributes; end
  ATTRIBUTES = ['title', 'authors', 'location',]
end

class LibraryBook < LibraryItem
  # ATTRIBUTES = LibraryItem::ATTRIBUTES
  ATTRIBUTES.push 'ISBN', 'pages'
end

class Foo
  ATTRIBUTES = ['title','authors','location']
end

class Bar < Foo
  ATTRIBUTES |= ['ISBN', 'pages']
end


pp LibraryItem::ATTRIBUTES
pp LibraryBook::ATTRIBUTES


pp Foo::ATTRIBUTES
pp Bar::ATTRIBUTES