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Smart Pointers and Interior Mutability

Rust

`Box`, `Rc`, `RefCell`, `Weak`, `Deref`, `Cow` — and the honest arena-vs-`Rc<RefCell<_>>` argument, taught arena-first so the interior-mutability cliff is a choice rather than a trap.

This track is written for Rust, which isn't the mode you're browsing in.

0 / 22 solved · 4 articles
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  1. 1. Not solved yet. The stack, the heap, and `Box<T>`
  2. 2. Not solved yet. Recursive types need indirection: E0072
  3. 3. Enum layout and niche optimization: why `Option<Box<T>>` is free Read
  4. 4. Not solved yet. `large_enum_variant`: boxing the fat variant
  5. 5. Not solved yet. `Rc<T>`: shared ownership by reference counting
  6. 6. Not solved yet. Inside `Rc`: `strong_count`, `ptr_eq`, `get_mut`, `try_unwrap`
  7. 7. Not solved yet. `Rc::make_mut`: copy-on-write shared data
  8. 8. Not solved yet. `Rc<str>`: interning without double indirection
  9. 9. Shared does not mean immutable Read
  10. 10. Not solved yet. `Cell<T>`: mutation by moving values in and out
  11. 11. Not solved yet. `RefCell<T>`: borrowing checked at runtime
  12. 12. Not solved yet. When `RefCell` panics: re-entrancy and borrows held too long
  13. 13. Not solved yet. `let _ =` versus `let _x =`: the guard that dies instantly
  14. 14. Not solved yet. RAII: build your own guard
  15. 15. Not solved yet. `Rc<RefCell<T>>`: the workhorse, and when it is a smell
  16. 16. Not solved yet. Reference cycles leak memory
  17. 17. Not solved yet. `Weak<T>`: non-owning references that break cycles
  18. 18. Not solved yet. `Rc::new_cyclic`: self-reference in one step
  19. 19. `Deref` is for smart pointers, and nothing else Read
  20. 20. Not solved yet. `OnceCell`: write-once interior mutability
  21. 21. Not solved yet. `static mut` is dead: what edition 2024 changed
  22. 22. Not solved yet. Indices as handles: the generational arena
  23. 23. Not solved yet. Bake-off: the same tree, an arena and an `Rc` graph
  24. 24. Not solved yet. Drop order in composite structures
  25. 25. Not solved yet. Build `Cell<T>` and `RefCell<T>` from scratch
  26. 26. Choosing a smart pointer Read

Check yourself

4 questions · one attempt each

These do not count toward finishing the track. They are here to catch the things that are easy to read past.

0 / 4

What does Rc::clone copy, and when is the value freed? 

let rc = Rc::new(5);
{ let _c = Rc::clone(&rc); Rc::strong_count(&rc) }
Rc::strong_count(&rc)
Question 1 of 4