rust_trait.rs

pub trait Bird {
    fn fly(&self);
}

pub struct Duck;
pub struct Swan;

impl Bird for Duck {
    fn fly(&self) {
        println!("duck fly");
    }
}

impl Bird for Swan {
    fn fly(&self) {
        println!("swan fly");
    }
}

pub fn get_trait_0(switch: bool) -> Box<dyn Bird> {
    if switch {
        Box::new(Swan)
    } else {
        Box::new(Duck)
    }
}

pub fn get_trait_1() -> impl Bird {
    let s = Swan;
    s
}

pub fn pass_bird_0(b: impl Bird) {
    b.fly();
}

pub fn pass_bird_1(b: &dyn Bird) {
    b.fly();
}

pub fn pass_bird_2<T>(b: T) -> ()
where
    T: Bird,
{
    b.fly();
}

fn main() {
    Box::new(Duck);
}