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Practical Experiences With Never Rewriting Software

Posted by Bob Warfield on October 29, 2007

Dharmesh Shah says we should (almost) never rewrite software, and he is right.  Rewrites come about, he says, from the following causes (the comments are mine):

1.  The Code Sucks:  Given who wrote the old code versus the new code, why won’t the new code suck too?  If your code is brittle, refactor it.  Fixing brittleness is one of things refactoring does, and it does so without breaking the world for a long time as a side effect.  If things are so bad refactoring won’t help, you probably need to rebuild the R&D team first and then they’ll insist the code be rewritten.  The prognosis is not good for this sort of thing, but sometimes you can recover.  Unfortunately, the fish rots from the head.  Who hired the original team?  Are they hiring the new team?  Is the company really prepared to hold position for a major rewrite and team rebuild.  This is dire experimental surgery that I hope you’ll avoid at all costs. 

2.  “We’re So Much Smarter Now”:  There is often a grain of truth here, but what will it do to your installed based to do a major rewrite that expunges what you see as flawed assumptions?  Note that you can refactor more than just code.  Refactor the user model.  Get it right without breaking the old ways.  You can be smarter without boiling the ocean.

3.  We Picked the Wrong Platform/Language:  I haven’t seen this one come up so often in the way Shah describes, where new guys hired in want a change.  We’ve tended to focus so much on good chemistry for communication purposes that we hire birds of a feather.  See my article on using fewer people to build better software for more.  However, sometimes platforms are forced on us, and Shah gives similar examples in his write up.  I can think of three major examples throughout my nearly 25 year career.  First was client server.  There was definitely a time to shift from using a desktop DB engine to client server on various projects I was aware of.   Next was Windows versus character-based DOS UI’s.  Lastly was the Internet.  These are all such radical paradigm shifts that unless you were amazingly prescient or just an amazing architect, you probably had to contemplate some major rewrite-level work to get there.  I have also presided over a langauge shift.  We ported Quattro Pro (the DOS version, Windows was in C++) from an unsupported (but reasonable mature) Modula-2 compiler to Turbo Pascal while at Borland.  The short story is it wasn’t worth it.  It took a lot of work despite how similar the languages were, and despite promises of how much better code Turbo Pascal would generate, the product actually ran a bit slower.  You’d have a hard time convincing me a rewrite to change languages was ever worth it.

I want to go back to the refactoring.  This is something I’ve always intuitively done.  We used to call it “interative middle-out programming”.  It’s the idea that you keep things running at all times and your changes are measured transformations.  Even testing can be approached in this way, although that’s the subject for another post.  I firmly believe that schedules and product roadmaps need to allocate refactoring time.  This is time spent that delivers no feature a product manager, customer, or sales person could recognize as such, but that improves the code.  Usually, not too much can be allocated there.  I strive to hold out 20% on top of whatever schedule pad is there, and yes, I will sacrifice that 20% if we fall behind.  About every 3rd or 4th major release, one must invest more, say 40% in housekeeping.

If you do all that, it is amazing how long a code base can remain viable.  The Modula-2 version of Quattro Pro on DOS lasted for well over 10 years with no signs of distress.  Like a house, the code must have good “bones”.  That is, the top-down architecture has to be right and can’t fight you too much.  But if you have those “good bones”, you can keep running with the same code base, add tons of functionality, and the team is amazingly much happier too.  Part of it is that the refactoring time let’s them exercise their computer science tendencies and not just work on yet another mundane feature.  All great developers need to scratch that itch.  They want to put a clever algorithm or structure in place.  It makes the code better, but it makes the team better to.  Part of it is rotating developers onto new projects if they get too bored.  Let the new young Turks have a shot.  Make sure the new guys know they’re the ones paying the bills.

So remember:  budget time for refactoring, and skip the major rewrite.  Everyone will be happier!

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3 Responses to “Practical Experiences With Never Rewriting Software”

  1. [...] unknown wrote an interesting post today on [...]

  2. [...] on his experience of porting Quattro Pro from Modula-2 compiler to Turbo Pascal, Bob Warfield, who commented on Dharmesh Shah’s post, believes, however, that it is not worth rewriting software to change languages. He also dds some [...]

  3. [...] recovered from a complete rewrite from assembler into C, Borland made the mistake with Arago and Quattro Pro  and Netscape’s complete rewrite of their Navigator 4 browser was a white-knuckle ride. In [...]

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