Code shared from the Rust Playground

playground.rs

enum IoState {
    Low,
    High,
    Floatit,
}

enum IoPin {
    AsOutput(Option<gpioa::PA8<Output<PushPull>>>),
    AsInput(Option<gpioa::PA8<Input<Floating>>>),
}

impl IoPin {
    fn as_input(&mut self) {
        match self {
            IoPin::AsOutput(p) => {
                let pin = core::mem::replace(p, None).unwrap();
                *self = IoPin::AsInput(Some(pin.into_floating_input()));
            }
            IoPin::AsInput(_) => {}
        };
    }

    fn as_output(&mut self, state: IoState) {
        match self {
            IoPin::AsOutput(Some(p)) => {pull_pin(p, state)}
            IoPin::AsInput(p) => {
                let mut pin = core::mem::replace(p, None).unwrap().into_push_pull_output();
                pull_pin(&mut pin, state);
                *self = IoPin::AsOutput(Some(pin));
            }
            _ => {}
        };
    }

    fn set_state(&mut self, state: IoState) {
        match state {
            IoState::Low | IoState::High => self.as_output(state),
            IoState::Floatit => self.as_input(),
        }
    }
}

fn pull_pin(pin: &mut gpioa::PA8<Output<PushPull>>, state: IoState) {
    match state {
        IoState::Low => {pin.set_low().unwrap()}
        IoState::High => {pin.set_high().unwrap()}
        IoState::Floatit => {}
    }
}

fn main() {

    let mut iopin = IoPin::AsInput(Some(gpioa.pa8.into_floating_input()));

    iopin.set_state(IoState::Floatit);
    iopin.set_state(IoState::Low);
    iopin.set_state(IoState::High);
}