#encoding #decoding


Isomorphic encoding/decoding data to & from numbers

4 releases

0.1.4 Jul 5, 2020
0.1.3 Jul 5, 2020
0.1.1 Jul 5, 2020
0.1.0 Jul 5, 2020

#691 in Encoding

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64 downloads per month
Used in finite_repr_derive

Custom license

372 lines

Finite Repr

This create exists to encode & decode data types with a finite number of representations. English please! Okay, okay, this crates allows you to convert your data types into numbers & back (or any other data type that implements FiniteValue), assuming the number of possible representations for that data type can be counted with the type you are encoding too.

Should You use this?

Probably not, probably just stick with serde.

Before you use this

This crate has alpha levels of reliablity & isn't likley to be the most efficent approach to encode data in your appplication.

It will also panic if you encode a large type into a small data type in some cases. While I do intend to address these issues I would encourage it's use at this point.

Okay but how do I use this...

I would recommend deriving the implementations, instead writing them by hand to ensure they're isomorphic & correct.

// If you choose to import it, this is how you would do so.
use finite_repr::{FiniteRepr, FiniteDecoding, FiniteEncoding};

#[derive(FiniteRepr, FiniteDecoding, FiniteEncoding)]
struct Character(pub RpgClass, pub Faction);

#[derive(FiniteRepr, FiniteDecoding, FiniteEncoding)]
enum RpgClass { Mage, Knight }

#[derive(FiniteRepr, FiniteDecoding, FiniteEncoding)]
enum Faction {

impl PartialEq for Character { /* ... */ }

fn main() {
  let my_character = Character(RpgClass::Mage, Faction::GoodGuys);
  let encoded = my_character.into_finite::<u16>();
  let decoded = encoded.and_then(Character::from_finite);

  // This assertion will be true.
  assert_eq!(Some(my_character), decoded);

Why does this exist?

This crate is the byproduct of bike shedding on a side project where finishing the project was optional. The main reason I deployed it on crates.io was to simplify reuse between my own projects.

Also I thought it would be fun to work on, but also I wanted a way to encode some data types with very limited possible representations in my game as numbers, as I was passing them through a trait object & couldn't make it generic.

Shortcomings of this crate

  • The code from the macros could be better.

  • The crate is likely misusing usize in FiniteRepr, & should probalby be replaced with a type whose size does not vary. I'll replace this eventually but atm I just want to start using this crate in my code.

  • No support for union types, it coudld probably be added but it just doesn't exist at this point in time.

  • It doesn't always gracefully handle failure in the event of an integer overflow.

  • This crate likely isn't suitable for encoding data that has a large amount of representations, such as a u128 or even (u32, u32).