Error Handling in Rust

Explore Rust's approach to error handling through the Option and Result types, and learn about error propagation.

By Kevin McAleer,    2 Minutes

Introduction

Error handling is a critical part of programming. Rust handles errors through its type system, specifically with the Option and Result types, rather than exceptions. This lesson explains how these types work and how they are used in Rust for error handling and propagation.

Learning Objectives

• Understand the Option and Result types and their purposes in Rust.
• Learn how to use these types for handling potential errors.
• Explore error propagation in Rust to create robust and safe applications.

Option and Result

The Option type is used in Rust when a value could be something or nothing (None). This type is used as a safer alternative to null references in other languages.

let some_number = Some(5);
let no_number: Option<i32> = None;

The Result type is used when operations could fail. It returns Ok(value) if the operation is successful, or Err(e) if it fails. This approach makes you explicitly handle errors, leading to more robust code.

fn divide(numerator: f64, denominator: f64) -> Result<f64, &'static str> {
    if denominator == 0.0 {
        Err("Cannot divide by zero")
    } else {
        Ok(numerator / denominator)
    }
}

Error Propagation

Instead of handling errors immediately, sometimes it’s more appropriate to propagate them to the calling code. Rust makes error propagation concise and safe with the ? operator.

fn get_divided_result(numerator: f64, denominator: f64) -> Result<f64, &'static str> {
    let result = divide(numerator, denominator)?;
    Ok(result)
}

The ? operator automatically propagates the error if the operation fails, simplifying error handling especially when multiple operations could fail.

Summary

In this lesson, you’ve learned about Rust’s approach to error handling using the Option and Result types and explored how these can be used to handle and propagate errors in a safe, explicit manner. Understanding and utilizing these concepts are fundamental in writing robust Rust applications.