b2.structs.md

title: Structs

⭐️ Structs are used to encapsulate related properties into one unified data type.

💡 By convention, the name of the struct should follow PascalCase.

There are 3 variants of structs,

1. C-like structs

• One or more comma-separated name:value pairs
• Brace-enclosed list
• Similar to classes (without its methods) in OOP languages
• Because fields have names, we can access them through dot notation

2. Tuple structs

• One or more comma-separated values
• A parenthesized list like tuples
• Looks like a named tuples

3. Unit structs

• A struct with no members at all
• It defines a new type but it resembles an empty tuple, ()
• Rarely in use, useful with generics

⭐️ When regarding OOP in Rust, attributes and methods are placed separately on structs and traits. Structs contain only attributes, traits contain only methods. They are getting connected via impls.

💡More complex examples can be found on impls & traits, lifetimes and modules sections.

C-like structs

// Struct Declaration
struct Color {
    red: u8,
    green: u8,
    blue: u8
}

fn main() {
  // Creating an instance
  let black = Color {red: 0, green: 0, blue: 0};

  // Accessing its fields using dot notation
  println!("Black = rgb({}, {}, {})", black.red, black.green, black.blue); //Black = rgb(0, 0, 0)

  // Structs are immutable by default, use `mut` to make it mutable but doesn't support field level mutability
  let mut link_color = Color {red: 0,green: 0,blue: 255};
  link_color.blue = 238;
  println!("Link Color = rgb({}, {}, {})", link_color.red, link_color.green, link_color.blue); //Link Color = rgb(0, 0, 238)

  // Copy elements from another instance
  let blue = Color {blue: 255, .. link_color};
  println!("Blue = rgb({}, {}, {})", blue.red, blue.green, blue.blue); //Blue = rgb(0, 0, 255)

  // Destructure the instance using a `let` binding, this will not destruct blue instance
  let Color {red: r, green: g, blue: b} = blue;
  println!("Blue = rgb({}, {}, {})", r, g, b); //Blue = rgb(0, 0, 255)

  // Creating an instance via functions & accessing its fields
  let midnightblue = get_midnightblue_color();
  println!("Midnight Blue = rgb({}, {}, {})", midnightblue.red, midnightblue.green, midnightblue.blue); //Midnight Blue = rgb(25, 25, 112)

  // Destructure the instance using a `let` binding
  let Color {red: r, green: g, blue: b} = get_midnightblue_color();
  println!("Midnight Blue = rgb({}, {}, {})", r, g, b); //Midnight Blue = rgb(25, 25, 112)
}

fn get_midnightblue_color() -> Color {
    Color {red: 25, green: 25, blue: 112}
}

Tuple structs

⭐️ When a tuple struct has only one element, we call it newtype pattern. Because it helps to create a new type.

struct Color(u8, u8, u8);
struct Kilometers(i32);

fn main() {
  // Creating an instance
  let black = Color(0, 0, 0);

  // Destructure the instance using a `let` binding, this will not destruct black instance
  let Color(r, g, b) = black;
  println!("Black = rgb({}, {}, {})", r, g, b); //black = rgb(0, 0, 0);

  // Newtype pattern
  let distance = Kilometers(20);
  // Destructure the instance using a `let` binding
  let Kilometers(distance_in_km) = distance;
  println!("The distance: {} km", distance_in_km); //The distance: 20 km
}

Unit structs

This is rarely useful on its own. But in combination with other features, it can become useful.

📖 ex: A library may ask you to create a structure that implements a certain trait to handle events. If you don’t have any data you need to store in the structure, you can create a unit-like struct.

struct Electron;

fn main() {
  let x = Electron;
}