gistfile1.txt

    fn toggle_between_A_and_B_while_keeping_value(&mut self) {
        *self = match self {
            E::A { value } => { E::B { value: mem::replace(value, S::dummy()) } }
            E::B { value } => { E::A { value: mem::replace(value, S::dummy()) } }
        };
    }