Function arg_combinators::opt_required_by

pub fn opt_required_by<T, E, F>(
    short: &str, 
    long: &str, 
    doc: &str, 
    hint: &str, 
    parse: F
) -> impl Arg<Item = T> where
    E: Clone + Debug + Display + Eq,
    F: Fn(String) -> Result<T, E>,