Hacker News Reader

It's only a terrible idea because our tools are terrible.

That's exactly the point!

(For example, if Rust would detect a version change, it could rewrite the data into a compatible format, etc.)

At which point you're not just memory mapping the file. And if the new version changes the size of the object, it doesn't pack in the same place in memory, so you have to repack before saving. Even serializing with versioning is very hard. Memory mapping is much worse. Several other comments indicate that I am not the only one with bad experiences here.

Reply on news.ycombinator.com