in reply to Why get() and set() accessor methods are evil
In your example you have a method (sub) called get_array. You have published an interface that says 'Whenever you invoke this method you will get an array to work with'. This is in effect a contract between you, the designer of the class and whoever uses your class. When the internal representation of the data changes to a hash, the get_array method will end up doing more work since it now needs to construct an array to pass back to the caller. Thus maintaining the contract and not causing problems.