gistfile1.rb

class Base
 class_attribute :my_array
 self.my_array = ['some_shared']
end

class Foo < Base
  self.my_array << 'some_foo'
end

class Bar < Base
  self.my_array << 'some_bar'
end

Foo.my_array #=> ['some_shared', 'some_foo', 'some_bar']
Bar.my_array #=> ['some_shared', 'some_foo', 'some_bar']

but I want

Foo.my_array #=> ['some_shared', 'some_foo']
Bar.my_array #=> ['some_shared', 'some_bar']