README.md

Using Structs to Structure Related Data¹

To run the program:

$ cargo run --bin using-structs
   Compiling using-structs v0.1.0 ...

Lessons learned

Defining and Instatiating Structs

Structs are very simple, basically a (nominal) set of name fields:

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

Otherwise, they work very similar to say, tuples, with some conveniences:

// Avoid typing active: active, email: email, sign_in_count: sign_in_count.
let user = User {
    active,
    email,
    sign_in_count,
};

// Avoid referencing every field manually when creating a new struct.
let user = User {
  sign_in_count: user.sign_in_count + 1,
  ..user
}

There are also tuple structs:

struct Color(i32, i32, i32);

You can also derive behavior, i.e. to use for debugging:

#[derive(Debug)]
struct Rectangle {
    width: u32,
    height: u32,
}
let rect = Rectangle {
    width: 30,
    height: 50,
};
dbg!(&rect);

Method Syntax

Using impl, we can define associated functions, or member-methods:

impl Rectangle {
  fn area(&self) -> u32 {
      self.width * self.height
  }

  fn square(size: u32) -> Self {
      Self {
          width: size,
          height: size,
      }
  }
}
println!("Rectangle's area is {}", rect.area());
let rect = Rectangle::square(10);
println!("Rectangle {:?}'s area is {}", rect, rect.area());

Footnotes

1. Source: https://doc.rust-lang.org/book/ch05-00-structs.html ↩