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// Recursive type using boxes
enum List {
Cons(i32, Box<List>),
Nil,
}
struct MyBox<T>(T);
impl<T> MyBox<T> {
fn new(x: T) -> MyBox<T> {
MyBox(x)
}
}
use std::ops::Deref;
impl<T> Deref for MyBox<T> {
type Target = T;
fn deref(&self) -> &T {
&self.0
}
}
fn main() {
// Storing `i32` value on heap
let b = Box::new(5);
println!("b = {}", b);
use crate::List::{Cons, Nil};
let list = Cons(1, Box::new(Cons(2, Box::new(Cons(3, Box::new(Nil))))));
// Dereferencing
let x = 5;
let y = &x;
assert_eq!(5, x);
assert_eq!(5, *y);
let x = 5;
let y = Box::new(x);
assert_eq!(5, x);
assert_eq!(5, *y);
let x = 5;
let y = MyBox::new(x);
assert_eq!(5, x);
assert_eq!(5, *y); // `*y` is equivalent to `*(y.deref())`
fn hello(name: &str) {
println!("Hello, {}", name);
}
// Deref coercion
let m = MyBox::new(String::from("Rust"));
// `&MyBox<String>` -> `&String` -> `&str`
hello(&m);
// `m`: MyBox<String>, `*m`: String, `(*m)[..]`: str, `&(*m)[..]`: &str
hello(&(*m)[..]);
}
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