In this lesson, we will talk about Structs in Rust

What are Structs?

Structs are a way to create more complex data types.

They are similar to tuples, but with a few differences.

For example, you can name the fields of a struct (and you can also define methods for structs).

If you prefer a video version

All the code is available on GitHub (link available in the video description)

Define a Struct

Let's say that we want to crete a User, with name, email, is_active and age. We can define a struct like this:



struct User {
    name: String,
    email: String,
    is_active: bool,
    age: u8,
}

And then you can create an instance of the struct like this:



struct User {
    name: String,
    email: String,
    is_active: bool,
    age: u8,
}

fn main() {
    let user = User {
        name: String::from("Jhon Doe"),
        email: String::from("doe@mail.com"),
        is_active: true,
        age: 25,
    };
}

Accessing Struct Fields

You can access the fields of a struct using dot notation:



struct User {
    name: String,
    email: String,
    is_active: bool,
    age: u8,
}

fn main() {
    let user = User {
        name: String::from("Jhon Doe"),
        email: String::from("doe@mail.com"),
        is_active: true,
        age: 25,
    };

    println!("User name: {}", user.name);
}

Explanaition:

We define a struct called User with four fields: name, email, is_active and age.
We create an instance of the struct and assign it to the user variable.
We access the name field of the user struct using dot notation (user.name).

Mutable Structs

You can make a struct mutable by using the mut keyword:



struct User {
    name: String,
    email: String,
    is_active: bool,
    age: u8,
}

fn main() {
    let mut user = User {
        name: String::from("Jhon Doe"),
        email: String::from("doe@mail.com"),
        is_active: true,
        age: 25,
    };

    user.name = String::from("Francesco");
    println!("User name: {}", user.name);

}

Note the you can't make individual fields of a struct mutable, you can only make the entire struct mutable.

Create a Struct instance using a function

You can create a function that returns a struct instance:



struct User {
    name: String,
    email: String,
    is_active: bool,
    age: u8,
}

fn main() {
    let user = create_user(String::from("Jhon Doe"), String::from("doe@mail"),);

    println!("User name: {}", user.name);
}

fn create_user(name: String, email: String,) -> User {
    User {
        name,
        email,
        is_active: true,
        age : 25,
    }
}

You can see the init shorthand syntax in the create_user function. This is a shorthand for initializing fields with variables that have the same name as the fields.

Creating Instances from Other Instances with Struct Update Syntax

You can create a new instance of a struct using another instance with the struct update syntax:



struct User {
    name: String,
    email: String,
    is_active: bool,
    age: u8,
}

fn main() {
    let user1 = User {
        name: String::from("Jhon Doe"),
        email: String::from("doe@mail.com"),
        is_active: false,
        age: 40
    };

    let new_user = User {
        name: String::from("Francesco"),
        email: user1.email,
        is_active: user1.is_active,
        age: user1.age,
    };

    println!("User name: {}", new_user.name);
}

In this example, we create a new instance of the User struct using the user1 instance with the struct update syntax.

Tuple Structs

Tuple structs are similar to regular structs, but their fields are not named:



struct Color(i32, i32, i32);
struct Point(i32, i32, i32);

fn main() {
    let black = Color(0, 0, 0);
    let origin = Point(0, 0, 0);
    println!("Black color: {}, {}, {}", black.0, black.1, black.2);
    println!("Origin: {}, {}, {}", origin.0, origin.1, origin.2);
}

In this example, we define two tuple structs: Color and Point. We create instances of these tuple structs and access their fields using dot notation.

Unit-Like Structs

You can define a struct with no fields, called a unit-like struct:



#[derive(Debug)]
struct User;

fn main() {
    let user = User;
    println!("User: {:?}", user);
}

Unit-like structs are useful when you need to implement a trait on a type but don't have any data to store in the type.

Conclusion

Structs are a way to create more complex data types in Rust. They are similar to tuples, but with a few differences. You can name the fields of a struct (and you can also define methods for structs). You can also make a struct mutable by using the mut keyword.

You can create a function that returns a struct instance. You can create a new instance of a struct using another instance with the struct update syntax. You can define tuple structs and unit-like structs.

I hope this lesson was useful. In the next lesson, we will see a practical example of using structs in Rust.

If you prefer a video version

All the code is available on GitHub (link available in the video description)

You can find me on https://francescociulla.com and on Twitter/X