Unit-only enums

Configurations typically use enums to support multiple values within a specific setting. To simplify this process, and to provide streamlined interoperability with Config, we offer a ConfigEnum trait and macro that can be derived for enums with unit-only variants.

#![allow(unused)]
fn main() {
#[derive(ConfigEnum)]
enum LogLevel {
	Info,
	Error,
	Debug,
	Off
}
}

When paired with Config, it’ll look like:

#![allow(unused)]
fn main() {
#[derive(Config)]
struct AppConfig {
	pub log_level: LogLevel
}
}

This enum will generate the following implementations:

• Provides a static T::variants() method, that returns a list of all variants. Perfect for iteration.
• Implements FromStr and TryFrom for parsing from a string.
• Implements Display for formatting into a string.

Attribute fields

The following fields are supported for the #[config] container attribute:

• before_parse - Transform the incoming string before parsing, so that loosely cased input still matches. Accepts the same case names as rename_all: lowercase, UPPERCASE, PascalCase, camelCase, snake_case, SCREAMING_SNAKE_CASE, kebab-case, and SCREAMING-KEBAB-CASE.

#![allow(unused)]
fn main() {
#[derive(ConfigEnum)]
#[config(before_parse = "kebab-case")]
enum ExampleEnum {
	// ...
}
}

With the above, very_high, VeryHigh, and VERY HIGH all parse into the same variant.

And the following for serde compatibility:

• rename
• rename_all - Has no default. Variant names are used exactly as written unless this is set.

Variants

The following fields are supported for the #[variant] variant attribute:

• fallback - Marks the variant as the fallback.

And the following for serde compatibility:

• alias
• rename - Overrides (explicitly sets) the string value used for parsing and formatting.

Deriving common traits

All enums (not just unit-only enums) typically support the same derived traits, like Clone, Eq, etc. To reduce boilerplate, we offer a derive_enum! macro that will apply these traits for you.

#![allow(unused)]
fn main() {
derive_enum!(
	#[derive(ConfigEnum)]
	enum LogLevel {
		Info,
		Error,
		Debug,
		Off
	}
);
}

This macro will inject the following attributes:

#![allow(unused)]
fn main() {
#[derive(Clone, Debug, Eq, PartialEq, serde::Deserialize, serde::Serialize)]
#[serde(rename_all = "kebab-case")]
}