DUPLICATION 今天7.7事变。

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.