Structs and Enums

Learn how to organize data using Rust's structs and enums, and understand how pattern matching works with these types.

By Kevin McAleer,    2 Minutes

Introduction

Structs and enums are the building blocks for creating new types in Rust’s type system. While structs allow you to create custom types that group related data together, enums enable you to define a type by enumerating its possible variants. This lesson explores how to define and use structs and enums, and introduces pattern matching.

Learning Objectives

• Understand how to define and use structs in Rust.
• Learn about enums and their role in Rust.
• Discover how pattern matching works in conjunction with enums.

Defining Structs

In Rust, a struct is a way to group related data together into a meaningful composite type. Each piece of data in the struct is called a ‘field’. Structs are similar to tuples, but each field has a name, providing more clarity.

struct User {
    username: String,
    email: String,
    sign_in_count: u64,
    active: bool,
}

Enums and Pattern Matching

Enums in Rust are types that can encompass different ‘variants’. Enums are particularly useful for defining a type which could be one of a few different variants. Combined with Rust’s pattern matching, enums are powerful for handling different scenarios.

enum Message {
    Quit,
    Move { x: i32, y: i32 },
    Write(String),
    ChangeColor(i32, i32, i32),
}

let msg = Message::Write(String::from("hello"));

Pattern matching in Rust allows you to compare a value against a series of patterns and execute code based on which pattern matches. It can be used with enums to handle different scenarios:

match msg {
    Message::Quit => {
        println!("The Quit variant has no data to destructure.");
    },
    Message::Move { x, y } => {
        println!("Move in the x direction {} and in the y direction {}", x, y);
    },
    Message::Write(text) => {
        println!("Text message: {}", text);
    },
    Message::ChangeColor(r, g, b) => {
        println!("Change the color to red {}, green {}, and blue {}", r, g, b);
    },
}

Summary

In this lesson, you learned about struct and enum types in Rust, how to define them, and how to use them in conjunction with pattern matching to handle different kinds of data and control flow in a type-safe way.