Additional Attributes

Strum supports several custom attributes to modify the generated code. At the enum level, the #[strum(serialize_all = "snake_case")] attribute can be used to change the case used when serializing to and deserializing from strings:

extern crate strum;
#[macro_use]
extern crate strum_macros;

#[derive(Debug, Eq, PartialEq, ToString)]
#[strum(serialize_all = "snake_case")]
enum Brightness {
    DarkBlack,
    Dim {
        glow: usize,
    },
    #[strum(serialize = "bright")]
    BrightWhite,
}

fn main() {
    assert_eq!(
        String::from("dark_black"),
        Brightness::DarkBlack.to_string().as_ref()
    );
    assert_eq!(
        String::from("dim"),
        Brightness::Dim { glow: 0 }.to_string().as_ref()
    );
    assert_eq!(
        String::from("bright"),
        Brightness::BrightWhite.to_string().as_ref()
    );
}

Custom attributes are applied to a variant by adding #[strum(parameter="value")] to the variant.

• serialize="...": Changes the text that FromStr() looks for when parsing a string. This attribute can be applied multiple times to an element and the enum variant will be parsed if any of them match.

• to_string="...": Similar to serialize. This value will be included when using FromStr(). More importantly, this specifies what text to use when calling variant.to_string() with the ToString derivation, or when calling variant.as_ref() with AsRefStr.

• default="true": Applied to a single variant of an enum. The variant must be a Tuple-like variant with a single piece of data that can be create from a &str i.e. T: From<&str>. The generated code will now return the variant with the input string captured as shown below instead of failing.

  // Replaces this:
  _ => Err(strum::ParseError::VariantNotFound)
  // With this in generated code:
  default => Ok(Variant(default.into()))

  The plugin will fail if the data doesn't implement From<&str>. You can only have one default on your enum.

• disabled="true": removes variant from generated code.

• message="..": Adds a message to enum variant. This is used in conjunction with the EnumMessage trait to associate a message with a variant. If detailed_message is not provided, then message will also be returned when get_detailed_message() is called.

• detailed_message="..": Adds a more detailed message to a variant. If this value is omitted, then message will be used in it's place.

• props(key="value"): Enables associating additional information with a given variant.