Abstraction and Variation

M aster, a friend told me today that I should never use the editor's copy-paste functions when programming , " said the young apprentice. " I thought the whole point of programming tools was to make our lives easier, " he continued. The Master stroked his long grey beard and pressed the busy button on his phone. This was going to be one of those long, important discussions. " Why do you think copy-pasting is wrong? " asked the Master. " Because I violate the DRY [don't repeat yourself] princi-ple? " replied the apprentice hesitantly. 1 " Exactly true, my young friend, " nodded the Master. " But it's so much easier to copy-paste code than to grapple with the alternatives, " continued the apprentice. The Master turned to his keyboard and typed " copy paste miner " in a search box. His memory was rapidly deteriorating, but luckily he could compensate by applying his formidable search skills on Google's planet-wide memory. He read aloud some key sentences from an article's abstract: 2 " CP-Miner uses data-mining techniques to efficiently identify copy-pasted code in large software suites and detects copy-paste bugs. Specifically, it takes less than 20 minutes for CP-Miner to identify 190,000 copy-pasted segments in Linux and 150,000 in FreeBSD. Moreover, CP-Miner has detected many new bugs in popular operating systems, 49 in Linux and 31 in FreeBSD. " The Master looked up from his screen, " Now that you've seen evidence of the extent and dangers of copy-pasting, let me ask you, are you sure you know all the appropriate alternatives? " " Of course I know them, " replied the disciple cockily. " Let's see. How do you handle two identical code sequences? " " I wrap the code up in a function or method. " " And if these functions are to execute subtly different code? " " Then I'll factor out the differences through Boolean or enumeration parameters I pass to them. I'll set the code in the function to follow different execution paths, based on these parameters. " " And if the differences concern data embedded in code? " " That's trivial; I'll simply pass those varying elements as parameters. " The Master was busily jotting down the ap-prentice's answers and his own ideas in a table (see table 1). He continued firing off questions. " And if the differences lie in the types …