#string #enums #flags #set #bit-flags #debugging


A string-enum and string-flags with fixed variants that can also accept arbitrary data

6 releases

0.3.1 Sep 26, 2023
0.3.0 Sep 26, 2023
0.2.2 Sep 24, 2023
0.1.1 Sep 19, 2023

#10 in #bit-flags


611 lines


A string-enum and string-flags with fixed variants that can also accept arbitrary data.

This is more extensible than traditional enums, bitflags or enumset, while being more ergonomic and more typo-resiliant than a set of strings like HashSet<String>.


str_flags! {
    pub Color: [

This Generates

pub struct Color(..)

And consts:

  • pub const Red: Color = "red";
  • pub const Green: Color = "green";
  • pub const DarkBlue: Color = "darkblue";

And auto implements

  • Debug, Clone, Eq, Hash
  • Display
  • FromStr
  • Borrow<str>
  • AsRef<str>
  • PartialEq<impl AsRef<str>>
  • Into<Flags<Self>>
  • BitOr<Output = Flags<Self>>
  • Serialize, with the serde feature enabled
  • Deserialize, with the serde feature enabled


You can create a Flags<Color> like this.


use the str_enum!() macro to opt out of flags related features.

let flags = Color::Red | Color::Green | Color::new("Yellow");


We stores all data in flatlowercase to avoid case mismatches and some typos.

Serialization and Deserialization

We use a string to serialize our "string enums".

e.g. "red"

We use a csv like string to serialize our Flags

e.g. "dog|cat|giraffe"

This ensures converting from enum to Flags does not break serialization formats.

The debug feature

Allowing any string to be an enum variant is obviously prone to typos. When the debug feature is enabled, we performs a fuzzy string check every time a comparison is made and emit a warn! though the log crate if similar strings are found. This is obviously slow so be careful when using this feature.


Currently we use EcoString which can only inline 15 bytes. Having a larger compile time constant string is a runtime error if the constant is USED.

A proc macro implementation in the future will address this issue.


~24K SLoC