⇒ A struct, or structure, is a custom data type that lets you package together and name multiple related values that make up a meaningful group.

Structs and Enums (discussed in Chapter 6) are the building blocks for creating new types in your program’s domain to take full advantage of Rust’s compile-time type checking.

Like tuples, the pieces of a struct can be different types. Unlike with tuples, in a struct you’ll name each piece of data so it’s clear what the values mean. Adding these names means that structs are more flexible than tuples: you don’t have to rely on the order of the data to specify or access the values of an instance.

• To define a struct, we enter the keyword struct and name the entire struct.
• Then, inside curly brackets, we define the names and types of the pieces of data, which we call *fields*.

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

Listing 5-1: A User struct definition

To use a struct after we’ve defined it, we create an instance of that struct by specifying concrete values for each of the fields. We create an instance by stating the name of the struct and then add curly brackets containing key: value pairs, where the keys are the names of the fields and the values are the data we want to store in those fields

In other words, the struct definition is like a general template for the type, and instances fill in that template with particular data to create values of the type. For example, we can declare a particular user as shown in Listing 5-2.

Filename: src/main.rs

fn main() {
    let user1 = User {
        active: true,
        username: String::from("someusername123"),
        email: String::from("[email protected]"),
        sign_in_count: 1,
    };
}

Listing 5-2: Creating an instance of the User struct

<aside> 📌 To get a specific value from a struct, we use dot notation. For example, to access this user’s email address, we use user1.email. If the instance is mutable, we can change a value by using the dot notation and assigning into a particular field.

</aside>

<aside> 📌 Note that the entire instance must be mutable; Rust doesn’t allow us to mark only certain fields as mutable.

</aside>

Returning Struct using fn()