The comments on yesterday's post on compatibility are pretty interesting.
There are effectively four options available when you find yourself a few versions into a platform and realize that you've made mistakes:
- Keep the mistakes, and potentially propogate those mistakes into other parts of the platform
- Rip out the mistakes, re-design the feature (sans mistakes) and accept the breaking change and broken apps
- Re-design the feature without the mistakes, add that re-designed feature to the product, deprecate the old broken feature, and accept duplication for some period of time until the older feature is ripped from the product
- Re-design the feature, add some elaborate compatibility mechanism to emulate the old behaviour, and sign up to maintain the elaborate compatibility mechanism for a long time
There may be some other options, but these are the ones that come to mind.
The comments from yesterday were in favour of (2).
I'm in favour of (3) as the primary model for making the product better, with a little bit of (2). I'm also willing to accept some of (1). I really dislike (4), as it doesn't benefit anyone in the long-term. (3) works well for individual APIs, but doesn't work well for whole sub-systems, such as the loader. If you change the loader in an incompatible way, you're really looking at options (2) or (4).
We've actually made a bunch of changes in Silverlight to improve the platform. As examples, we've removed non-generic collections, and have changed the way String comparisons work. We also changed the binder pretty significantly. Not to mention a new security system ... Oh, and we also included a stripped down XMLReader/Writer!
Compatibility is a tough balance relative to product evolution. We've been discussing this exact issue a lot over the last year, and the best way to evolve the project forward. The trick is coming up with a model that you really life, doesn't hugely impact the engineering process, doesn't inhibit product evolution going forward, and is explainable to customers. Taking submissions now ...