protean

A flexible data enum guaranteeing strict variant ordering for backward-compatible binary serialization.

Why?

I found myself making a similar data type quite often for serialized communication of flexible values. At the same time, when working with serialization formats that are not self-describing, reordering enum variants is a footgun that is easy to overlook. This crate has strict tests to maintain variant ordering.

Features

• Assertions to protect backward compatibility.
• Safe methods for checked conversion of integer/float types.
• Cow for slice-type variants (Bytes and Text) for zero-copy deserialization.
• (serde feature) De/serialization via serde.
• (owned feature) Self-referential OwnedDataCell which supports deserializing from an owned buffer without copying, using the yoke crate.

It's surprisingly hard to do zero-copy deserialization from an owned buffer right, as you essentially need a 'self lifetime to borrow from self, which requires either Box::leak(...) or Pin<Box<...>> to get a static lifetime. Then, once you have a static lifetime to self-referenced data, you need to narrow the static lifetime to preserve soundness. Thankfully yoke handles the safety of self-reference and lifetime narrowing which avoids needing to manually ensure soundness of self-referential data.

License

Licensed under the MIT license.