Hiring guide for Rust Engineers

Rust Developer Hiring Guide

Rust is a high-level, multi-paradigm, general-purpose programming language designed for performance and safety. It was developed by Mozilla Research to improve the speed, prevent segmentation faults and guarantee thread safety. Rust supports functional as well as imperative-procedural paradigms. One of the unique features of Rust is its ownership system which helps in managing memory safely without needing garbage collection. This makes it particularly suitable for systems programming tasks traditionally written in C or C++. Rust also emphasizes zero-cost abstractions, minimal runtime and improved productivity with tooling like automatic code formatting and an integrated test suite. Its rich type system enforces at compile time many properties that other languages might catch with runtime assertions. In addition to its memory safety guarantees, Rust also offers safe concurrency or parallelism - this means you can have multiple tasks running simultaneously without any undefined behavior or data races. Overall, while being complex due to these advanced features; once mastered it provides a level of performance control similar to lower-level languages but with higher-level ergonomics.

Ask the right questions secure the right Rust talent among an increasingly shrinking pool of talent.

First 20 minutes

General Rust app knowledge and experience

The first 20 minutes of the interview should seek to understand the candidate's general background in Rust application development, including their experience with various programming languages, databases, and their approach to designing scalable and maintainable systems.

How would you declare a mutable variable in Rust?
You can declare a mutable variable in Rust using the 'mut' keyword. For example, 'let mut x = 10;' declares a mutable variable 'x' with an initial value of 10.
What are the primitive data types in Rust?
Rust has several primitive data types including integers (i32, u32, i64, u64, isize, usize), floating-point numbers (f32, f64), Booleans (bool), characters (char), and tuples.
Describe the difference between 'const' and 'static' in Rust.
'const' and 'static' both allow you to define global variables, but with a key difference. 'const' is a constant value, which means it's a value that's read-only and cannot be changed. 'static', on the other hand, is a variable that's stored in the static memory of the program and it's available for the entire duration the program runs.
How would you handle error in Rust?
Error handling in Rust is primarily done through the Result and Option types. The Result type is used for functions that can return an error, and the Option type is used for functions that can return a null value.
What is the use of 'match' in Rust?
'match' is a keyword in Rust used for pattern matching. It allows you to compare a value against a series of patterns and then execute code based on which pattern matches.
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What you’re looking for early on

Does the candidate have a solid understanding of Rust's unique features?
Has the candidate demonstrated the ability to write clean, efficient Rust code?
Is the candidate familiar with Rust's tooling and ecosystem?
Can the candidate effectively debug Rust code and handle errors?

Next 20 minutes

Specific Rust development questions

The next 20 minutes of the interview should focus on the candidate's expertise with specific backend frameworks, their understanding of RESTful APIs, and their experience in handling data storage and retrieval efficiently.

How would you define a function in Rust?
Functions in Rust are defined using the 'fn' keyword. For example, 'fn add(a: i32, b: i32) -> i32 { a + b }' defines a function named 'add' that takes two parameters of type i32 and returns an i32.
What are traits in Rust?
Traits in Rust are a way to define shared behavior across types. They are similar to interfaces in other languages. You can use traits to define shared behavior in your own types.
Describe the difference between 'String' and '&str' in Rust.
'String' is a growable, mutable, owned, heap-allocated data structure. On the other hand, '&str' is a slice pointing to some UTF-8 string data, which is usually in a String or a string literal.
How would you implement concurrency in Rust?
Rust provides several tools for concurrency including threads, the 'channel' function for message passing, and 'Mutex' and 'Arc' for shared state. The standard library provides a 'thread' module containing the 'spawn' function, which can be used to create new threads.
What is 'ownership' in Rust?
Ownership is a key feature of Rust that makes it possible to manage memory safely without a garbage collector. It's a set of rules that the compiler checks at compile time, which includes no garbage value, no dangling reference, and efficient memory usage.
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The ideal back-end app developer

What you’re looking to see on the Rust engineer at this point.

At this point, a skilled Rust engineer should demonstrate strong problem-solving abilities, proficiency in Rust programming language, and knowledge of software development methodologies. Red flags include lack of hands-on experience, inability to articulate complex concepts, or unfamiliarity with standard coding practices.

Digging deeper

Code questions

These will help you see the candidate's real-world development capabilities with Rust.

What does the following Rust code do?
fn main() {
    let x = 5;
    let y = x + 1;
    println!("{}", y);
This code declares a variable x with the value of 5, then declares another variable y which is the value of x plus 1. It then prints the value of y to the console, which will be 6.
What will be the output of the following Rust code?
fn main() {
    let s = String::from("Hello");
    println!("{}", s);

fn takes_ownership(some_string: String) {
    println!("{}", some_string);
This code will not compile because the ownership of the string s is moved to the function takes_ownership, and then we try to print s which is no longer valid.
What does the following Rust code do?
fn main() {
    let mut v = vec![1, 2, 3, 4, 5];
    println!("{:?}", v);
This code declares a mutable vector v with the values 1 through 5, then pushes the value 6 onto the end of the vector. It then prints the vector to the console, which will be [1, 2, 3, 4, 5, 6].
What does the following Rust code do?
use std::thread;

fn main() {
    let handle = thread::spawn(|| {
        "Hello from a thread!"

    println!("{}", handle.join().unwrap());
This code creates a new thread that returns the string 'Hello from a thread!'. The main thread waits for the new thread to finish and prints the result.

Wrap-up questions

Final candidate for Rust Developer role questions

The final few questions should evaluate the candidate's teamwork, communication, and problem-solving skills. Additionally, assess their knowledge of microservices architecture, serverless computing, and how they handle Rust application deployments. Inquire about their experience in handling system failures and their approach to debugging and troubleshooting.

Describe the difference between 'borrowing' and 'slicing' in Rust.
Borrowing is a mechanism in Rust that allows you to have multiple references to the same data without copying it. Slicing, on the other hand, is a way to take a reference to a portion of a collection rather than the whole thing.
How would you use 'lifetimes' in Rust?
Lifetimes are a way of ensuring that all references are valid. They are used to prevent 'dangling references'. The syntax for lifetimes is an apostrophe followed by a name, like 'a.
What is 'cargo' in Rust?
Cargo is the package manager for Rust. It allows you to do many things like building your project, downloading libraries your project depends on, and building those libraries. It's also used to run tests.

Rust application related

Product Perfect's Rust development capabilities

Beyond hiring for your Rust engineering team, you may be in the market for additional help. Product Perfect provides seasoned expertise in Rust projects, and can engage in multiple capacities.