Derive Macro FieldlessEnumConstType

#[derive(FieldlessEnumConstType)]
{
    // Attributes available to this derive:
    #[const_type]
}

Available on crate feature derive only.

Derives the const type for a fieldless enum as well as the implementations of the Const and OptionallyConst traits for the parameterizations of the const type that represent the enum variants.

Example

use optionally_const::OptionallyConst;
use optionally_const_macros::FieldlessEnumConstType;

#[derive(FieldlessEnumConstType, Debug)]
#[const_type(ConstTypeName)]
enum FieldlessEnum {
    A,
    B,
    C,
}

fn print_fieldless_enum<T>(value: T)
where
    T: OptionallyConst<FieldlessEnum>,
{
    if let Some(value) = T::MAYBE_CONST {
        println!("Const value: {:?}", value);
    } else {
        let value: FieldlessEnum = T::into_value(value);
        println!("Non-const value: {:?}", value);
    }
}

fn main() {
    print_fieldless_enum(FieldlessEnum::A);
    print_fieldless_enum(FieldlessEnum::B);
    print_fieldless_enum(FieldlessEnum::C);
    print_fieldless_enum(ConstTypeName::<{ FieldlessEnum::A as usize }>);
    print_fieldless_enum(ConstTypeName::<{ FieldlessEnum::B as usize }>);
    print_fieldless_enum(ConstTypeName::<{ FieldlessEnum::C as usize }>);
}