[tetrep]

If you want to future proof it you need to version it. It sounds like you're trying to pack many things into a single file, so having the first few bits of the file represent a version allows you to use fixed length integers without fear of them being too small (in the future). You can reserve the "last" version for varint if you truly need it.

In general, I find adding versions to things allows for much more graceful future redesigns and that is, IMO, invaluable if you're concerned about longevity and are not confident in your ability to perfectly design something for the indefinite future.

[NavinF]

I don't see the point. As soon as you bump the version number, old versions of the software will refuse to read newer files. So you might as well use a new format and file extension for the newer files. Of course the new software will read both formats.

The way protobufs handles versioning (old software ignores unknown fields) is far superior and realistically everyone uses 64 bit fixed length sizes everywhere

[paulddraper]

YAGNI

The idea is so simple that any change would be a misfeature.

[stravant]

I'm a big YAGNI proponent but format version numbers are not something I would dare to YAGNI.

[paulddraper]

Even if it's varint separated messages?

[catiopatio]

You stick a magic number and a version number at the top of the file and call it done. It’s trivial and buys you a great deal.

The magic means it’s possible to identify the file type. Maybe you’ll add a tool later that operates on multiple types of files.

The version means you can evolve the contents in non-backwards-compatible ways, while maintaining the ability to read/parse the old version.

It’s a pain in the ass to add a magic or version number later; there’s a reason why nearly every file format on the planet has both.

[paulddraper]

> nearly every file format on the planet

XML

JSON

YML

TOML

[catiopatio]

  <?xml version="1.1" encoding="UTF-8" ?>

The others are serialization formats, like protobuf — they’re not file formats.