newtype_playground.rs

struct Animal {};

type Cat = Animal;
type Dog = Animal;

impl ToString for Animal {
  fn to_string(&self) -> String {
    "Animal".to_string()
  }
}

impl ToString for Cat {
  fn to_string(&self) -> String {
    "Cat".to_string()
  }
}

impl ToString for Dog {
  fn to_string(&self) -> String {
    "Dog".to_string()
  }
}

fn main() {
  
  let animal = Animal {};
  
  // "Animal"
  println!("{:}", animal);
  
  // "Cat"
  println!("{:}", animal as Cat);
  
  // "Dog"
  println!("{:}", animal as Dog);
  
}