Rust: Converting between Enums and Strings

enum_str.rs

pub enum Foo {
    A,
    B,
}

impl Foo {
    pub fn variants() -> impl Iterator<Item = Foo> {
        array::IntoIter::new([Self::A, Self::B])
    }
}

impl fmt::Display for Foo {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match self {
            Foo::A => write!(f, "a"),
            Foo::B => write!(f, "b"),
        }
    }
}

impl FromStr for Foo {
    type Err = String;

    fn from_str(s: &str) -> Result<Self, Self::Err> {
        Self::variants()
            .find(|x| x.to_string() == s)
            .ok_or_else(|| format!("Unknown option: `{}`", s))
    }
}