Rust 문법: dyn, trait, polymorphism

Rust

Using Trait Objects That Allow for Values of Different Types - The Rust Programming Language

 

1. dyn, trait

trait: unknown 타입 (Self)을 위해 정의된 메서드 collection

doc.rust-lang.org/book/ch10-02-traits.html?highlight=trait#traits-defining-shared-behavior

dyn: dynamic 하게 dispatch 되는 부분을 highlight

(dynamic dispatch to a trait object)

 

2.  예제 코드

자바/파이썬 개념으로 설명하면

Car, Motocycle이란 클래스가 있고 이 두 클래스는 Vehicle이란 interface를 implement 한다.

각 go()를 실행하면 단순히 message만 출력한다.

 

Shop이란 클래스는 자동차 종류를 vector(array) 형식으로 저장하고 있다. type은 Vehicle

Box를 이용해서 pointer 변수이다. Shop에 Car, Motorcycle들을 append 시킨다.

 

move_all을 실행하면 polymorphism 하게 모든 Vehicle를 implement 한 클래스들의 go()를 실행한다. 

// A trait is a collection of methods defined for an unknown type: Self.
// They can access other methods declared in the same trait.

// The dyn keyword is used to highlight that calls to methods on the associated
// Trait are dynamically dispatched. To use the trait this way, it must be 'object safe'.

trait Vehicle {
    fn go(&self);
}

struct Car;
struct Motorcycle;

impl Vehicle for Car {
    fn go(&self) {
        println!("Hello, Car is moving!");
    }
}

impl Vehicle for Motorcycle {
    fn go(&self) {
        println!("Hello, Motorcycle is moving!");
    }
}

impl Car {
    fn new() -> Car {
        Car
    }
}

impl Motorcycle {
    fn new() -> Motorcycle {
        Motorcycle
    }
}

struct Shop {
    cars: Vec<Box<dyn Vehicle>>,
}

impl Shop {
    fn new() -> Shop {
        Shop { cars: Vec::new() }
    }

    fn add_car(&mut self, car: Box<dyn Vehicle>) {
        self.cars.push(car);
    }

    fn move_all(&self) {
        for car in &self.cars {
            car.go();
        }
    }
}

fn main() {
    let mut shop = Shop::new();
    shop.add_car(Box::new(Car::new()));
    shop.add_car(Box::new(Motorcycle::new()));

    shop.move_all();

    // let mut vec: Vec<Box<dyn Vehicle>> = vec![];
    // let car = Car::new();
    // let motor = Motorcycle::new();

    // vec.push(Box::new(car));
    // vec.push(Box::new(motor));

    // for vehicle in &vec {
    //     vehicle.go();
    // }
}

 

# 결과
Hello, Car is moving!       
Hello, Motorcycle is moving!