I am Joannes Vermorel, founder at Lokad. I am also an engineer from the Corps des Mines who initially graduated from the ENS.

I have been passionate about computer science, software matters and data mining for almost two decades. (RSS - ATOM)

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Refactoring and logistics ("L'intendance suivra!")

With Eclipse and VS2005, refactoring is now a standard feature of modern IDEs. No more than few minutes are now sufficient to drastically change the internal structure of a software library. Yet, if software logistics cannot keep the pace then productivity bottlenecks of software evolution remain unchanged. De Gaulle said L'intendance suivra! (which could be poorly translated by "Logistics always keep up!"). Yet many european wars have been lost due to poor logistics, and, back to the discussion, I believe that logistics is no less important in software matters than it is in wars.

By software logistics I mean all processes required to keep the whole thing running when changing the structure of a component; and, in particular, the issues related to upstream and downstream dependencies (deployement issues are left to a later post).

Upstream dependencies include all the components that you are relying on. Well, changing your code does not impact the components you are relying on, right? Wrong. Just consider serialization as a simple counter-example (your code evolves and let all existing data unreadable). Upstream issues are not serialization-specific, the very same problem exists with structured database storage (yes, versioning SQL queries is a pain too). More the generally, I am not aware of any refactoring tool providing any support to tackle data persistence issues. Although version tolerance features do exists in .Net 2.0 (but the framework is still lacking very simple features such as field renaming). I am really looking forward the tools that will (one day) provide persistence-aware refactoring capabilities.

Downstream dependencies include all the components that rely on your's. It's clear that any change you do (at least for any publicly exposed method/object) can break the downstream dependencies. The don't break anything approach is a killing approach in terms of software evolution (the most interesting case being don't fix bugs, our customers rely on them). But on the other hand, assuming that L'intendance suivra! ("we don't care, RTFM!") is not realistic. IMO, the present best practice is to provide an awful lot of documentation to facilitate the upgrade (see Upgrading WordPress for a good example). Yet providing such documentation is expensive and the ROI is low (because contrary to the code that has been improved, such documentation will not be leveraged in future developments). The solution, IMO again, lies in better refactoring tools that include some downstream-awareness. It would be possible to generate some "API signature patch" (the generation being a process as automated as possible) that could be applied by the client on its own code. Well, I am also really looking forward for such kind of tools.

Reader Comments (1)

Really great blog post. It was very well written and thought out, Thanks" rel="nofollow">:)

October 11, 2009 | Unregistered CommenterSerenity
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