// Define a trait named `Speak`
// with a single method `speak`.
trait Speak {
    fn speak(&self);
}

// Define a struct named `Human`.
struct Human {
    name: String,
}

// Implement the `Speak` trait for the `Human` struct.
impl Speak for Human {
    fn speak(&self) {
        println!("Hello, my name is {}.", self.name);
    }
}

// Define a struct named `Dog`.
struct Dog {
    name: String,
}

// Implement the `Speak` trait for the `Dog` struct.
impl Speak for Dog {
    fn speak(&self) {
        println!("Woof! My name is {}.", self.name);
    }
}

fn main() {
    // Create instances of `Human` and `Dog`.
    let person = Human {
        name: String::from("Alice"),
    };
    let dog = Dog {
        name: String::from("Buddy"),
    };

    // Call the `speak` method, which is
    // implemented via the `Speak` trait.
    person.speak();
    dog.speak();

    // Alternatively, use a function that takes
    // a reference to a `Speak` trait object.
    introduce_speaker(&person);
    introduce_speaker(&dog);
}

fn introduce_speaker(speaker: &dyn Speak) {
    speaker.speak();
}