RefCell overview in Rust - Mini Project: Build & Apply

RefCell overview

📖 Scenario: Imagine you have a box that you want to share with your friends. Sometimes, you want to let one friend change what's inside the box, but other times, many friends can look inside without changing it. Rust's RefCell helps you do this safely at runtime.

🎯 Goal: You will create a simple Rust program using RefCell to hold a number. You will learn how to borrow it immutably (to read) and mutably (to change) safely.

📋 What You'll Learn

Create a RefCell holding an integer value

Borrow the value immutably to print it

Borrow the value mutably to change it

Print the changed value

💡 Why This Matters

🌍 Real World

RefCell is useful when you want to change data inside something that is normally immutable, like inside shared objects or GUI state.

💼 Career

Understanding RefCell helps you write safe Rust code that needs interior mutability, common in systems programming and application development.

1

Create a RefCell holding the number 10

Write a line to create a variable called value that is a RefCell holding the integer 10. Use std::cell::RefCell.

Rust

use std::cell::RefCell;

fn main() {
    // Create a RefCell called value holding 10
    // Your code here
}

Hint

Use RefCell::new(10) to create the RefCell.

2

Borrow the value immutably to print it

Add a line to borrow value immutably using borrow() and print the number inside with println!. Use val as the variable name for the borrowed reference.

Rust

use std::cell::RefCell;

fn main() {
    let value = RefCell::new(10);
    // Borrow value immutably and print it
    // Your code here
}

Hint

Use value.borrow() to get an immutable reference, then print with println!("Value is: {}", *val).

3

Borrow the value mutably to change it

Add code to borrow value mutably using borrow_mut() and change the number inside to 20. Use val_mut as the variable name for the mutable borrow.

Rust

use std::cell::RefCell;

fn main() {
    let value = RefCell::new(10);
    let val = value.borrow();
    println!("Value is: {}", *val);
    // Borrow value mutably and change it to 20
    // Your code here
}

Hint

Use value.borrow_mut() to get a mutable reference, then assign 20 to *val_mut.

4

Print the changed value

Add a line to borrow value immutably again and print the updated number with println!. Use val as the variable name for the borrowed reference.

Rust

use std::cell::RefCell;

fn main() {
    let value = RefCell::new(10);
    let val = value.borrow();
    println!("Value is: {}", *val);
    let mut val_mut = value.borrow_mut();
    *val_mut = 20;
    // Borrow value immutably again and print the new value
    // Your code here
}

Hint

Borrow immutably again with value.borrow() and print the new value.