Hey there! If you’re prepping for a Rust interview, you’re in the right place. I’ve put together a mix of basic, coding, advanced, and behavioral questions to help you nail it. Let’s dive in!
Table of Contents
Basic Rust Interview Questions
Q1: What’s the deal with ownership rules in Rust?
Answer: Ownership is Rust’s secret sauce for memory safety without needing a garbage collector. Here’s the rundown:
- Every value has one owner—like a VIP pass to memory.
- When that owner goes out of scope, Rust cleans up the memory automatically. No fuss, no muss.
- You can pass ownership to someone else (called a “move”) or let others peek at it temporarily (borrowing), either immutably or mutably.
It’s all about keeping things tidy and safe!
Q2: How does move differ from copy in Rust?
Answer:
- Move: Think of it like handing over the keys to your car. Ownership transfers, and the original variable can’t use it anymore.
- Copy: This is just for simple stuff like numbers or booleans that implement the Copy trait. It’s like making a photocopy—both versions stick around.
Here’s an example:
rust
let x = String::from("hello");
let y = x; // x gives up ownership to y, so x is done
// println!("{}", x); // Nope, this would error! Q3: What’s borrowing all about in Rust?
Answer: Borrowing is like borrowing a book from a friend—you get to read it, but you don’t own it. In Rust, it’s temporary access to a value without taking it over.
Check this out:
rust
fn print_str(s: &String) {
println!("{}", s);
}
let s = String::from("hello");
print_str(&s); // s is borrowed here, still good to use after Q4: Mutable vs. immutable borrowing—what’s the difference?
Answer:
- Immutable Borrowing (&): You can have as many read-only peeks as you want, but no changes allowed.
- Mutable Borrowing (&mut): Only one borrower at a time, and they can tweak the data.
Here’s a quick demo:
rust
let mut s = String::from("hello");
let r1 = &s; // immutable borrow
let r2 = &s; // another immutable borrow—totally fine
// let r3 = &mut s; // Nope! Can’t mutate while others are borrowing Rust Coding Interview Questions
Q5: How would you reverse a string in Rust?
Answer: Here’s a clean way to flip a string:
rust
fn reverse_string(s: &str) -> String {
s.chars().rev().collect()
}
fn main() {
let input = "hello";
println!("{}", reverse_string(input)); // Prints "olleh"
} It’s simple: break the string into characters, reverse them, and glue them back together!
Q6: How do you find the largest number in an array?
Answer: Rust makes this a breeze with iterators:
rust
fn find_largest(arr: &[i32]) -> i32 {
*arr.iter().max().unwrap()
}
fn main() {
let numbers = [3, 5, 9, 1, 4];
println!("Largest number: {}", find_largest(&numbers)); // 9
} The unwrap() assumes there’s at least one number—otherwise, it’d panic.
Q7: Can you whip up a linked list in Rust?
Answer: Sure thing! Here’s a basic take using Rc and RefCell for flexibility:
rust
use std::rc::Rc;
use std::cell::RefCell;
struct Node {
value: i32,
next: Option<Rc<RefCell<Node>>>,
}
impl Node {
fn new(value: i32) -> Rc<RefCell<Node>> {
Rc::new(RefCell::new(Node { value, next: None }))
}
} This sets up a node you can link up later. Rust’s safety rules make this trickier than in other languages, but it’s doable!
Q8: How about a thread-safe counter?
Answer: Let’s use Arc and Mutex to keep things safe across threads:
rust
use std::sync::{Arc, Mutex};
use std::thread;
fn main() {
let counter = Arc::new(Mutex::new(0));
let mut handles = vec![];
for _ in 0..10 {
let counter = Arc::clone(&counter);
let handle = thread::spawn(move || {
let mut num = counter.lock().unwrap();
*num += 1;
});
handles.push(handle);
}
for handle in handles {
handle.join().unwrap();
}
println!("Final count: {}", *counter.lock().unwrap()); // Should be 10
} Each thread bumps the counter, and Mutex ensures no one steps on anyone else’s toes.
Q9: How would you code the Fibonacci sequence recursively?
Answer: Here’s a classic recursive Fibonacci:
rust
fn fibonacci(n: u32) -> u32 {
match n {
0 => 0,
1 => 1,
_ => fibonacci(n - 1) + fibonacci(n - 2),
}
}
fn main() {
println!("Fibonacci(10): {}", fibonacci(10)); // 55
} It’s straightforward but not super efficient for big numbers—something to keep in mind!
Q10: How does Rust keep memory safe without a garbage collector?
Answer: Rust pulls this off with some clever tricks:
- Ownership: One boss per value, and when they’re done, the memory’s freed.
- Borrow Checker: It’s like a referee making sure no one messes up references or races for data.
- RAII: Resources get cleaned up automatically when they’re no longer needed.
No garbage collector, just strict rules that work like magic.
Rust Advanced Topics interview
Q11: What are lifetimes in Rust?
Answer: Lifetimes are Rust’s way of making sure references don’t outlive what they point to. Here’s an example:
rust
fn longest<'a>(s1: &'a str, s2: &'a str) -> &'a str {
if s1.len() > s2.len() { s1 } else { s2 }
} The ‘a says both inputs and the output share the same lifespan—no dangling pointers allowed!
Q12: What’s the scoop on smart pointers?
Answer: Smart pointers give you more control over memory:
- Box<T>: Puts stuff on the heap with single ownership.
- Rc<T>: Lets multiple owners share something via reference counting.
- RefCell<T>: Sneaky way to mutate data even when it’s borrowed immutably.
They’re like tools in your Rust toolbox for different jobs.
Q13: What’s up with async/await in Rust?
Answer: Async lets Rust handle tasks without blocking, using async and .await:
rust
async fn fetch_data() -> String {
"Hello, async!".to_string()
}
#[tokio::main]
async fn main() {
let data = fetch_data().await;
println!("{}", data);
} You’ll need a runtime like Tokio to make it work—it’s perfect for I/O-heavy stuff!
Q14: How does Rust fit into blockchain?
Answer: Rust is a rockstar in blockchain (think Solana or Substrate) because:
- It’s fast—no garbage collection slowing things down.
- It’s safe—fewer bugs and exploits.
- It handles concurrency like a champ, great for blockchain nodes.
You might use it for smart contracts with frameworks like Anchor on Solana.
Behavioral & Problem-Solving Questions
Q15: How do you make Rust code run faster?
Answer: Here are some pro tips:
- Use iter() for loops instead of indexing—it’s slicker.
- Try Cow<T> (Clone-on-Write) to save memory when you don’t need copies.
- Cut down on heap allocations where you can.
- Profile with cargo flamegraph to spot bottlenecks.
It’s all about working smarter, not harder!
