How do I implement hierarchical traits?

Question

I have two traits in a hierarchy: Animal and Bird. How can I create a Chicken that implements Bird?

trait Animal {
    fn noise(&self) -> String;
    fn print_noise(&self) {
        print!("{}", self.noise());
    }
}

trait Bird: Animal {
    fn noise(&self) -> String {
        "chirp"
    }
}

struct Chicken {}

impl Bird for Chicken {}

playground

When I try to compile, I get:

error[E0277]: the trait bound `Chicken: Animal` is not satisfied
  --> src/lib.rs:16:6
   |
16 | impl Bird for Chicken {}
   |      ^^^^ the trait `Animal` is not implemented for `Chicken`

I don't want to implement Animal before Bird, because I want Chicken to inherit the noise function from Bird.

Answer 1

Simple answer: you can't. Rust doesn't have inheritance by design. Rust doesn't have same object-oriented model as Java or C++.

If you really want to do something like this, you can implement one trait for another with this code

trait Animal {
    fn noise(&self) -> String;
    fn print_noise(&self) {
        print!("{}", self.noise());
    }
}

trait Bird:Animal {}

impl<T: Bird> Animal for T {
    fn noise(&self) -> String {
        "chirp".to_string()
    }
}


struct Chicken {}

impl Bird for Chicken {}

fn main() {
    let chicken = Chicken{};
    chicken.print_noise();
}

As others, I would suggest reading The Rust Programming Language book, specifically OOP and Traits and Generics sections. It's free when reading online.