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Add to speaker notes rc.md (#366)

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* Update rc.md

* Fix wording and formatting

* Update rc.md

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Co-authored-by: Andrew Walbran <qwandor@google.com>
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Charisee Chiw 2023-02-26 18:05:01 -08:00 committed by GitHub
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src/std/rc.md
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@ -28,9 +28,12 @@ fn main() {
<details>
* `Rc`'s Count ensures that its contained value is valid for as long as there are references.
* Like C++'s `std::shared_ptr`.
* `clone` is cheap: creates a pointer to the same allocation and increases the reference count.
* `clone` is cheap: it creates a pointer to the same allocation and increases the reference count. Does not make a deep clone and can generally be ignored when looking for performance issues in code.
* `make_mut` actually clones the inner value if necessary ("clone-on-write") and returns a mutable reference.
* Use `Rc::strong_count` to check the reference count.
* Compare the different datatypes mentioned. `Box` enables (im)mutable borrows that are enforced at compile time. `RefCell` enables (im)mutable borrows that are enforced at run time and will panic if it fails at runtime.
* You can `downgrade()` a `Rc` into a *weakly reference-counted* object to
create cycles that will be dropped properly (likely in combination with
`RefCell`).