Structs

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

How to define

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

let user1 = User {
  email: String::from("some@email.com"),
  username: String::from("someuser"),
  active: true,
  sign_in_count: 1,
};
// if mutable,
let mut user1 = User {
  email: String::from("some@email.com"),
  username: String::from("someuser"),
  active: true,
  sign_in_count: 1,
};
user1.email = String::from("another@email.com");

Rust doesn't allow us to mark only certain fields as mutable. (The entire instance must be mutable.)

fn build_user(email: String, username: String) -> User {
  User {
    email: email,
    username: username,
    active: true,
    sign_in_count: 1,
  }
}

fn build_user_shorthand(email: String, username: String) -> User {
  User {
    email, // same name in struct
    username,
    active: true,
    sign_in_count: 1,
  }
}

Creating Instances From Other Instances With Struct Update Syntax

let user2 = User {
  email: String::from("another@email.com"),
  usename: String::from("user2"),
  ..user1
};

Creates an instance in user2 that has a different value for email, username but has the same values for the active and sign_in_count fileds from user1.

Using Tuple Structs without Named Fields to Create Different Types

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

let black = Color(0,0,0);
let origin = Point(0,0,0);

Unit-Like Structs Without Any Fields

can also define structs that don't have any fields.

() : canbe useful in situations in which you need to implement a trait on some type but don't have any data that you want to store in the type itself.