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

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