On Thu, Apr 28, 2011 at 10:00 AM, Evan Laforge
It's been remarked to me that relying on the Binary and Serialize classes is dangerous, because there's no guarantee they won't maintain a consistent format. So if my app uses the Serialize instances that come with cereal, it could suddenly fail to read old saves after an upgrade to cereal.
However, neither binary nor cereal expose the underlying serialization algorithms for various types except through the instances, so I would have to copy and paste the code over if I want control over it. If I don't trust 'instance Serialize String' to not change behind my back, maybe I could at least trust 'Data.Serialize.stringToUtf8' to not change since if it did the name would now be wrong.
Are these fears justified? I imagine if the Int instance for Serialize changed there would be an uproar and it would probably have to be changed back. I sent a bug to the maintainers of data-binary a long time ago about the Double instance not serializing -0, and they ignored it, probably because it would be bad to change the instance. So can I use the included instances without fear of them changing between releases? Of course I still run the risk of an instance from some other package changing, but I'm less likely to be using those.
When I need to comply with a specific binary format, I never rely on Binary/Serialize class instances - I always fall back on the primitive operations on Words of varying sizes (perhaps defining my own type classes for convenience). The 'Builder' type makes this pretty easy. If I were writing binary data to disk, in my mind that would fall under "complying with a specific binary format". I do, however, rely on the SafeCopy class (or the equivalent Happstack.Data.Serialize class) to be able to read it's own data back from persistent storage - it is a specific design goal of the library and the library has version support built in. If the authors of the library come up with a better way to store maps, I would expect them to bump the version tag for the stored data and provide automatic migration for old data. Antoine