Code shared from the Rust Playground

playground.rs

pub enum Index<'a> {
  S(&'a str),
  I(usize),
}

impl<'a> From<&'a str> for Index<'a> {
  fn from(s: &'a str) -> Self {
    Self::S(s)
  }
}

impl<'a> From<String> for Index<'a> {
  fn from(s: String) -> Self {
    Self::S(s.as_str())
  }
}