Smart Pointer Structs

Box, Rc, Arc และอื่นๆ

Box

fn main() {
    // Box - heap allocation
    let boxed = Box::new(42);
    println!("Boxed: {}", boxed);

    // Deref
    let value: i32 = *boxed;
    println!("Unboxed: {}", value);

    // Recursive types need Box
    #[derive(Debug)]
    enum List {
        Cons(i32, Box<List>),
        Nil,
    }

    let list = List::Cons(1,
        Box::new(List::Cons(2,
            Box::new(List::Cons(3,
                Box::new(List::Nil))))));

    println!("List: {:?}", list);

    // Box for trait objects
    trait Animal {
        fn speak(&self) -> &str;
    }

    struct Dog;
    impl Animal for Dog {
        fn speak(&self) -> &str { "woof" }
    }

    let animal: Box<dyn Animal> = Box::new(Dog);
    println!("Animal says: {}", animal.speak());

    // Box::leak for 'static
    let leaked: &'static str = Box::leak(String::from("forever").into_boxed_str());
    println!("Leaked: {}", leaked);
}