How to Pass a Rust Interview: Top Questions

Online Python Trainer for Beginners

Learn Python easily without overwhelming theory. Solve practical tasks with automatic checking, get hints in Russian, and write code directly in your browser — no installation required.

Start Course

Introduction: Why is Rust so demanding in interviews?

Rust is a systems programming language renowned for its memory safety and high performance. The Rust compiler is strict but fair: it will not allow an ownership error or a dangling reference. That's why in Rust interviews, syntax is rarely asked "by the book." Instead, interviewers test a deep understanding of the memory model, resource management, and idiomatic code.

In this article, we will break down the top 10 questions most frequently asked in interviews for Junior and Middle Rust developers. Each question comes with an explanation and a code example. If you are preparing for an interview, this article will be your checklist.

1. Ownership and Borrowing

This is the foundation of Rust. Without understanding ownership, you will not pass the interview. An interviewer might ask you to explain the difference between String and &str or ask why some code does not compile.

Question: Explain what ownership is and how data transfer works in functions.

Answer: In Rust, every value has exactly one owner. When a variable goes out of scope, the value is dropped. Passing a value to a function means a move of ownership, unless the type implements the Copy trait.

fn main() {    let s1 = String::from("hello");    let s2 = s1; // s1 is moved to s2    // println!("{}", s1); // Error! s1 no longer owns the string    println!("{}", s2);}

If you want to pass data without losing ownership, use references (&):

fn main() {    let s1 = String::from("hello");    let len = calculate_length(&s1); // borrowing    println!("The length of '{}' is {}.", s1, len);}

fn calculate_length(s: &String) -> usize {    s.len()}

Question: What is mutable borrowing and why can there only be one?

Answer: Mutable borrowing (&mut) allows you to change a value through a reference. The compiler guarantees that there is only one mutable reference in scope to prevent data races.

fn main() {    let mut s = String::from("hello");    let r1 = &mut s;    // let r2 = &mut s; // Error! Cannot have two mutable references    r1.push_str(", world");    println!("{}", r1);}

2. Lifetimes

Lifetimes are what scare beginners. In an interview, you will be asked to explain why 'a annotations are needed and how the compiler infers lifetimes.

Question: When do you need to explicitly specify lifetimes?

Answer: When a function returns a reference, and the compiler cannot determine on its own how long it will live. A classic example is a function that returns the longest of two strings:

fn longest<'a>(x: &'a str, y: &'a str) -> &'a str {    if x.len() > y.len() { x } else { y }}

fn main() {    let string1 = String::from("long string");    let result;    {        let string2 = String::from("short");        result = longest(&string1, &string2);    }    // println!("{}", result); // Error! string2 is dropped, reference is dangling}

The annotation 'a says: "the lifetime of the returned reference is equal to the shorter of the lifetimes of the input references."

Question: What is elision (lifetime elision rules)?

Answer: The compiler automatically inserts lifetimes in simple cases. If a function takes one reference and returns a reference, the lifetime is inferred. If there are multiple input references, you need to specify them explicitly.