读书笔记 – The Evils of Duplication

Most people assume that maintenance begin when an application is released, that maintenance means fixing bugs and enhancing features, We think these people are wrong. Programmers are constantly in maintenance mode. Our understanding changes day by day. New requirements arrive as we’re designing or coding. Perhaps the environment changes. Whatever the reason, maintenance is not a discrete activity, but a routine part of the entire developments process.

When we perform maintenance, we have to find and change the representations of thins – those capsules of knowledge embedded in the application, The problem is that it’s easy to duplicate knowledge in the specifications, processes, and programs that we develop, and when we do so, we invite a maintenance nightmare – one that starts well before the application ships.

We feel that the only way to develop software reliably, and to make our developments easier to understand and maintain, is to follow what we call the DRY principle:

  EVERY PIECE OF KNOWLEDGE MUST HAVE A SINGLE, UNAMBIGUOUS, AUTHORITATIVE REPRESENTATION WITHIN A SYSTEM.

Why do we call it DRY?

  DRY – Don’t Repeat Yourself

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