pub trait InputPin {}
pub trait OutputPin {}

pub trait IoPin {
    type Input: InputPin + IoPin<Input = Self::Input, Output = Self::Output>;
    type Output: OutputPin + IoPin<Input = Self::Input, Output = Self::Output>;

    fn into_input(self) -> Self::Input;
    fn into_output(self) -> Self::Output;
}

struct Port<P1, P2> {
    p1: P1,
    p2: P2
}

struct Pin;
impl InputPin for Pin {}
impl OutputPin for Pin {}

fn main() {

}

fn some_function<P1, P2>(port: &mut Port<P1, P2>)
where
    P1: IoPin,
    P2: IoPin
{
    let _p1 = port.p1.into_output();
}