Defining and instantiating structs are two important concepts in Rust. To define a struct, we use the `struct` keyword and then specify the name of the struct and the names and types of the fields. To instantiate a struct, we create a variable of the struct type and then specify the values for each of the fields. For example, the following code defines a struct called `User` with four fields:
struct User {
active: bool,
username: String,
email: String,
sign_in_count: u64,
}
To instantiate a `User` struct, we can use the following code:
let user1 = User {
active: true,
username: String::from("someusername123"),
email: String::from("someone@example.com"),
sign_in_count: 1,
};
We can then access the values of the `User` struct using dot notation. For example, the following code prints the value of the `email` field of the `user1` struct:
println!("{}", user1.email);
We can also change the values of the fields of a `User` struct using dot notation. For example, the following code changes the value of the `email` field of the `user1` struct:
user1.email = String::from("anotheremail@example.com");
We can also construct a new instance of a struct as the last expression in the function body to implicitly return that new instance. For example, the following function constructs a new `User` struct and returns it:
fn build_user(email: String, username: String) -> User {
User {
active: true,
username: username,
email: email,
sign_in_count: 1,
}
}
This function can then be used to create new `User` structs, as shown in the following code:
let user1 = build_user(String::from("someone@example.com"), String::from("someusername123"));
