pub trait SymPair { fn sym_pair(self) -> (Option<Robj>, Robj); }
fn sym_pair(self) -> (Option<Robj>, Robj)
impl<S, R> SymPair for (S, R) where S: AsRef<str>, R: Into<Robj>,
impl<S, R> SymPair for &(S, R) where S: AsRef<str>, R: Into<Robj>, R: Clone,