Is it possible to parameterize traits over self mode?

[bblum]

I have no idea if this is theoretically easy or impossible or what. But consider this trait from my design for select:

trait SelectPort<T> {
    fn recv_ready(self) -> Option<T>;
}

This takes self by value because for a oneshot port, it has to consume the endpoint. But for a stream port, you might not be allowed to have it by value at all, but still expect to be able to select on it. It would be nice to have:

trait SelectPort<T, selfmode> {
    fn recv_ready(selfmode) -> Option<T>;
}

and then:

impl <T> SelectPort<T, self> for PortOne<T> ...
impl <T> SelectPort<T, &mut self> for Port<T> ...

[alexcrichton]

Couldn't this already be implemented with something like

trait SelectPort<T> {
    fn recv_ready(self) -> Option<T>;
}

impl <T> SelectPort<T> for PortOne<T> {
  ...
}
impl <'self, T> SelectPort<T> for &'self mut Port<T> {
  ...
}

In the second one you're not really consuming self?

[bblum]

Good point. I should do that.