How do you cleanly separate code for backwards compatibility from the main code?

Question

I'm interested in what strategies people have come up with for separating all the crufty logic that's necessary to maintain backwards compatibility from the main code of an application. In other words, strategies that let you come closer to having your code look as if there were no backwards compatibility concerns except for separate isolated source files distinctly for that task.

For example, if your application reads a particular file format, instead of one giant honking file parsing function, you could have your code first iterate a list of "quirks" entries/objects, where each quirk checks the file to see if it's a file it would apply to, and if so invokes its own parsing logic instead of the normal case logic.

Quirks is an OK strategy but you have to do work to put hooks in for quirks checks at all the appropriate places in your app, and what the checks will look like will vary for different quirk types, etc. It almost seems like there should be libraries dedicated to the boilerplate for this task. Another issue is how to enforce that quirks aren't abused as general purpose hooks into arbitrary chunks of the app.

Answer 1

My usual strategy is to have something separate that will translate the backward compatibility input into the new implementation input, and then use the new implementation code with this translated data.