Code shared from the Rust Playground

playground.rs

use std::marker::PhantomData;

trait ConnT<T> {
    type Res;
    fn proc(T) -> Self::Res;
}

struct Conn1;
impl<T> ConnT<T> for Conn1 {
    type Res = Result<T, ()>;
    fn proc(res: T) -> Self::Res {
        Ok(res)
    }
}

struct Conn2;
impl<T> ConnT<T> for Conn2 {
    type Res = Option<T>;
    fn proc(res: T) -> Self::Res {
        Some(res)
    }
}

struct Pub<Adapt> (PhantomData<Adapt>);

impl<C> Pub<C> {
    pub fn get(&self, req: &str) -> String {
        println!("{}", req);
        ("1".to_string())+req
    }
}

impl<C> Pub<C> 
{
    pub fn check1(&self) -> C::Res
        where C: ConnT<String>
    {
        C::proc(self.get("1"))
    }

    pub fn check2(&self) -> C::Res
        where C: ConnT<u32>
    {
        C::proc(self.get("1").parse().unwrap())
    }
}

fn main() {
    let p1:Pub<Conn1> = Pub(PhantomData);
    let p2:Pub<Conn2> = Pub(PhantomData);
    let res = p1.check1();
    println!("{:?}", res);
    let res = p1.check2();
    println!("{:?}", res);
    let res = p2.check1();
    println!("{:?}", res);
    let res = p2.check2();
    println!("{:?}", res);
}