Practices of an Agile Developer

  32   Substitute by Contract

“Deep inheritance hierarchies are great. If you need functionality from some other class, just inherit from it! And don’t worry if your new class breaks things; your callers can just change their code. It’s their problem, not yours.”

A key way to keep systems flexible is by letting new code take the place of existing code without the existing code knowing the difference. For instance, you might need to add a new type of encryption to a communications infrastructure or implement a better search algorithm using the ...