Chapter 6. Duplication

Note

“You can say that again!”

Duplication has been recognized for more than 30 years as the bane of the programmer's lot. How does duplication cause problems?

  • There is more code to maintain (a conceptual and physical burden).

  • Parts that vary are buried inside the parts that stay the same (a perceptual problem—it's hard to see the important stuff).

  • Code variations often hide deeper similarities—it will be hard to see the deeper solution among all the similar code.

  • There's a tendency to fix a bug in one place and leave identical bugs elsewhere unfixed. When you see two variations of something, it's hard to know which variation is the right pattern or if there's a good reason for the variations.

David Parnas introduced the idea of ...

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