Smart Pointers

let b = Box::new(5);
*b  // 5

use std::rc::Rc;
let a = Rc::new(1);
let b = Rc::clone(&a);
Rc::strong_count(&a)  // 2

use std::cell::RefCell;
let c = RefCell::new(1);
*c.borrow_mut() += 1;
*c.borrow()  // 2

use std::sync::{Arc, Mutex};
let m = Arc::new(Mutex::new(1));
*m.lock().unwrap() += 1;
*m.lock().unwrap()  // 2

use std::borrow::Cow;
fn add_hi(s: Cow<str>) -> Cow<str> {
    if s.contains("hi") { s } else { format!("{s} hi").into() }
}
add_hi("x".into())  // "x hi"

let s: &'static str = Box::leak(String::from("x").into_boxed_str());
s  // "x"

use std::rc::{Rc, Weak};
let strong = Rc::new(1);
let w: Weak<_> = Rc::downgrade(&strong);
w.upgrade().map(|r| *r)  // Some(1)

// use std::pin::Pin;
// Pin<&mut T> after ensuring immovable

fn f(n: &i32) -> i32 { *n }
f(&Box::new(3))  // 3

use std::cell::Cell;
let c = Cell::new(1);
c.set(2);
c.get()  // 2

use std::rc::Rc;
use std::cell::RefCell;
let n = Rc::new(RefCell::new(0));
*n.borrow_mut() = 5;
*n.borrow()  // 5

fn go() -> Result<(), Box<dyn std::error::Error>> {
    Ok(())
}
go().is_ok()  // true

use std::mem::ManuallyDrop;
let m = ManuallyDrop::new(String::from("x"));
// must not double-free if you take inner

struct Node { v: i32, next: Option<Box<Node>> }
let n = Node { v: 1, next: None };
n.v  // 1

use std::sync::Arc;
let a = Arc::new(vec![1, 2]);
let b = a.clone();
b.len()  // 2