RefCell overview in Rust - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a new RefCell containing the value 5.

Rust

let value = std::cell::[1]::new(5);

Drag options to blanks, or click blank then click option'

ARefCell

BCell

CMutex

DRc

Attempts:

3 left

💡 Hint

Common Mistakes

Using Cell instead of RefCell, which has different borrowing rules.

Using Rc which is for reference counting, not interior mutability.

The RefCell type allows mutable borrowing checked at runtime. Here, RefCell::new(5) creates a new RefCell holding the value 5.

2fill in blank

medium

Complete the code to borrow the value immutably from the RefCell.

Rust

let value = std::cell::RefCell::new(10);
let borrowed = value.[1]();

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Aborrow_mut

Bborrow

Cget

Dclone

Attempts:

3 left

💡 Hint

Common Mistakes

Using borrow_mut() when only an immutable borrow is needed.

Trying to use get(), which is not a method of RefCell.

The borrow() method immutably borrows the value inside the RefCell. It returns a smart pointer that enforces borrowing rules at runtime.

3fill in blank

hard

Fix the error in the code to mutably borrow the value inside the RefCell.

Rust

let cell = std::cell::RefCell::new(20);
let mut_ref = cell.[1]();

Drag options to blanks, or click blank then click option'

Aborrow_mut

Bborrow

Cget_mut

Dclone

Attempts:

3 left

💡 Hint

Common Mistakes

Using borrow() instead of borrow_mut() for mutable access.

Trying to use get_mut(), which is not available on RefCell.

The borrow_mut() method mutably borrows the value inside the RefCell. Using borrow() would only give an immutable borrow and cause a compile-time or runtime error if mutable access is needed.

4fill in blank

hard

Fill both blanks to create a RefCell, mutably borrow its value, and change it.

Rust

let cell = std::cell::[1]::new(30);
let mut val = cell.[2]();
*val = 40;

Drag options to blanks, or click blank then click option'

ARefCell

Bborrow

Cborrow_mut

DCell

Attempts:

3 left

💡 Hint

Common Mistakes

Using Cell instead of RefCell, which has different borrowing rules.

Using borrow() instead of borrow_mut() when trying to mutate.

First, create a RefCell with RefCell::new(30). Then, mutably borrow the value with borrow_mut() to change it.

5fill in blank

hard

Fill all three blanks to create a RefCell, borrow it immutably, and print the value.

Rust

let cell = std::cell::[1]::new(50);
let val = cell.[2]();
println!("Value is: {}", *[3]);

Drag options to blanks, or click blank then click option'

ACell

Bborrow

Cval

DRefCell

Attempts:

3 left

💡 Hint

Common Mistakes

Using Cell instead of RefCell.

Trying to print the RefCell itself instead of the borrowed value.

Create a RefCell with RefCell::new(50). Then immutably borrow it with borrow(). Finally, dereference val to print the inner value.