实现 Unsafe Trait

trait Pet {
    fn talk(&self) -> String;

    fn greet(&self) {
        println!("Oh you're a cutie! What's your name? {}", self.talk());
    }
}

struct Dog {
    name: String,
    age: i8,
}

impl Pet for Dog {
    fn talk(&self) -> String {
        format!("Woof, my name is {}!", self.name)
    }
}

fn main() {
    let fido = Dog { name: String::from("Fido"), age: 5 };
    fido.greet();
}

To implement Trait for Type, you use an impl Trait for Type { .. } block.
Unlike Go interfaces, just having matching methods is not enough: a Cat type with a talk() method would not automatically satisfy Pet unless it is in an impl Pet block.
Traits may provide default implementations of some methods. Default implementations can rely on all the methods of the trait. In this case, greet is provided, and relies on talk.