two_legs.rs

two_legs.rs

// The feature that Rust needs

trait Animal { const LEGS: u32; }

fn walk_on_your_two_legs<A>(_animal: &A)
where A: Animal
// , A::LEGS == 2 :(
{
    println!("I'm walking on my two legs")
}

struct Human { }
impl Animal for Human { const LEGS: u32 = 2; }

struct Dog { }
impl Animal for Dog { const LEGS: u32 = 4; }

fn main() {
    let tintin = Human { };
    let snowy = Dog { };
    
    walk_on_your_two_legs(&tintin);
    walk_on_your_two_legs(&snowy);
}