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Maintaining multiple copies of instance variables and instance methods makes software development and maintenance difficult as you try to correct bugs, add features, improve performance, and change behavior. Adding multiple programmers and multiple years to the mix turns mere difficulty into certain failure.
Of course, with just two new minutes instance variables about which
to worry, you could cope. In a more complex example, every kind of
entertainment—from football to opera—would have a minutes
instance variable, as well as a variety of other instance variables.