Rust enum with attached strings

playground.rs

use std::slice::Iter;
use std::collections::HashSet;

trait EnumValues : Sized {
    fn values() -> Iter<'static, Self>;
}

macro_rules! simple_enum {
    ($name:ident { $(($item:ident, $repr:expr),)* }) => {
        #[derive(Debug)]
        enum $name {
        $(
            $item,
        )*
        }
        
        use std::fmt;
        impl fmt::Display for $name {
           fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
                write!(f, "{}", match self {
                $(
                  &$name::$item => $repr,
                )*
                })
            }
        }
        
        use std::str::FromStr;
        impl FromStr for $name {
            type Err = ();
            fn from_str(s: &str) -> Result<$name, ()> {
                match s {
                $(
                  $repr => Ok($name::$item),
                )*
                  _ => Err(()),
                }
            }
        }
        
        impl EnumValues for $name {
            fn values() -> Iter<'static, $name> {
              static VALUES: &'static [$name] = &[$($name::$item),*];
              VALUES.into_iter()
            }
        }
    }
}

simple_enum!{
Foo {
 (A, "a"),
 (B, "b"),
}
}

fn main() {
  let s = Foo::values().map(|v| v.to_string()).collect::<HashSet<String>>();
  for v in Foo::values() {
    println!("{} ({:?}): {}", v, v, s.contains(&v.to_string()));
  }
}