Rust Interview Questions

(This article provides a curated list of interview questions that were asked to me, covering key Rust concepts. It aims to assist you in preparing for Rust-related interviews, focusing on areas like memory management, ownership, concurrency, and more.)

Introduction

Rust is known for its focus on memory safety, concurrency, and performance, making it one of the most sought-after languages in the tech industry. As a systems programming language, Rust is often used in high-performance applications, from web assembly to operating systems. Preparing for a Rust interview requires a deep understanding of the language's core principles and features.

These questions summarize those asked during various Rust-based interviews. I will update them periodically.

Basics of Rust

1. What is Rust, and where is it mostly used?

   • Rust’s key features like memory safety, concurrency without data races, and zero-cost abstractions. Common use cases such as systems programming, web assembly, blockchain, and embedded systems.

2. What are ownership and borrowing in Rust? Explain with examples.

   • Ownership rules, borrowing (&T, &mut T), the relationship between ownership and references, examples of valid and invalid ownership transfers.

3. What are lifetimes in Rust? Explain with examples.

   • The purpose of lifetimes, how they ensure memory safety, named lifetimes ('a), lifetime annotations in structs and functions, and examples to demonstrate their usage.

4. What is the process of how memory is allocated for a String type in Rust?

   • Stack and heap memory allocation, String metadata (pointer, length, capacity), resizing a string, and how Rust manages deallocation.

5. What is &str in Rust, and where is it stored?

   • &str is a string slice — an immutable view into a UTF-8 sequence. It can point to:
     • Static memory ("literal") in the binary
     • Heap memory (when sliced from a String)
     • Embedded data via include_str!()
   • It's a fat pointer (*const u8 + length) and does not own the data it references.

Concurrency and Asynchronous Programming

5. What are async and await in Rust?

   • Rust’s approach to asynchronous programming, async functions returning Future objects, and examples demonstrating usage with executors.

6. Explain Tokio and where it is used.

   • The Tokio runtime, its role in managing asynchronous tasks, features like timers and I/O, and its usage in high-performance applications.

7. What is pinning in Rust, and why is it important?

   • Pinning to ensure that memory locations remain fixed, its necessity for self-referential types, and examples related to asynchronous programming.

Error Handling and Unsafe Code

8. How do we handle errors in Rust?

   • Error handling with Result, Option, and the ? operator. Idiomatic practices for error propagation and structured error handling with crates like thiserror or anyhow.

9. How does the ? operator simplify error handling in Rust? Provide an example.

   • The syntax and use of ? for early returns in functions, combining it with Result and Option for concise error propagation.

10. What is unsafe Rust? Explain with an example.

    • Scenarios where unsafe code is needed, such as manual memory management or FFI. Example of unsafe blocks demonstrating dereferencing raw pointers.

Advanced Concepts

11. What are generics in Rust? Explain with examples.

    • Using generics for type abstraction in functions, structs, and enums. Example of generics combined with traits to enforce type constraints.

12. How do you implement inheritance in Rust?

    • Rust’s trait system as an alternative to classical inheritance, example of trait-based polymorphism, and composition over inheritance.

13. What is Zero-Cost Abstraction?

    • Explanation of how Rust achieves abstraction without runtime overhead, with examples of iterators, traits, and function calls being compiled to efficient machine code.

Memory Management and Safety

14. What is the possibility of memory leaks in Rust?

    • Reference cycles with Rc and Arc, how they lead to memory leaks, and the use of Weak to prevent them.

15. What are Smart Pointers? Explain about Box, Rc, Arc.

    • The functionality of Box for heap allocation, Rc for reference counting in single-threaded contexts, and Arc for atomic reference counting in multi-threaded contexts.

16. What is RefCell and how does it enable interior mutability in Rust? Provide an example.

    • Interior mutability with RefCell, runtime borrowing checks, and examples of how it allows mutating data even when the struct is immutable.

17. How do you implement a shared, mutable global counter using Rc<RefCell> in Rust?

    • You can use Rc<RefCell> to create a counter that multiple parts of a single-threaded program can own and mutate. Rc enables shared ownership, and RefCell allows interior mutability checked at runtime.

      Example:

      use std::rc::Rc;
      use std::cell::RefCell;
      
      fn main() {
          let counter = Rc::new(RefCell::new(0));
          let counter1 = Rc::clone(&counter);
          let counter2 = Rc::clone(&counter);
      
          *counter1.borrow_mut() += 1;
          *counter2.borrow_mut() += 2;
      
          println!("Counter value: {}", counter.borrow()); // prints 3
      }
      

    • What is Cow and how is it used in Rust?

      • The Cow (Clone on Write) type for optimizing memory usage, scenarios where it avoids cloning, and examples of using Cow with str and Vec.

    • Explain deadlocks concerning Rust.

      • How deadlocks can occur with mutexes in multi-threaded programs, examples of cyclic resource dependencies, and strategies to avoid deadlocks.

    ---

    Conclusion

    These questions cover a variety of fundamental topics essential for understanding Rust's capabilities and best practices, and are commonly asked in interviews.