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// Recursive type using boxes
use std::rc::Rc;
use std::cell::RefCell;
#[derive(Debug)]
enum List {
Cons(Rc<RefCell<i32>>, Rc<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
}
}
struct CustomSmartPointer {
data: String,
}
impl Drop for CustomSmartPointer {
fn drop(&mut self) {
println!("Dropping CustomSmartPointer with data `{}`!", self.data);
}
}
fn main() {
// Storing `i32` value on heap
let b = Box::new(5);
println!("b = {}", b);
use crate::List::{Cons, Nil};
let list = Cons(Rc::new(RefCell::new(1)),
Rc::new(Cons(Rc::new(RefCell::new(2)),
Rc::new(Cons(Rc::new(RefCell::new(3)),
Rc::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)[..]);
let c = CustomSmartPointer {
data: String::from("my stuff"),
};
let d = CustomSmartPointer {
data: String::from("other stuff"),
};
println!("CustomSmartPointer created.");
drop(c);
println!("CustomSmartPointer dropped before the end of main.");
let value = Rc::new(RefCell::new(5));
let a = Rc::new(Cons(Rc::clone(&value), Rc::new(Nil)));
let b = Cons(Rc::new(RefCell::new(3)), Rc::clone(&a));
let c = Cons(Rc::new(RefCell::new(4)), Rc::clone(&a));
*value.borrow_mut() += 10;
println!("a after = {:?}", a);
println!("b after = {:?}", b);
println!("c after = {:?}", c);
}
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