Shared via Rust Playground

playground.rs

struct Nat { val: u32}
impl Nat {
   fn set(&mut self, x: u32) {self.val = x}
   fn get(&self) -> u32 {self.val}
}

struct Pos { val: u32}
impl Pos {
   fn set(&mut self, x: u32){self.val = x}
   fn get(&self) -> u32 {self.val}
}

trait NatPos {}
impl NatPos for Nat{}
impl NatPos for  Pos{}

fn main() {
   let mut w  = Nat {val:1};
   let mut x = &w as &NatPos;
   // let z : Pos = &x;
   // {
   //       let mut y : Nat : &x;
   //    y.set(0);
   // }
   // fprint("Positive integer: {}", z.get()); 
}