Structs and Enums

struct User { id: u32, name: String }
let u = User { id: 1, name: "Ada".into() };
u.id  // 1

#[derive(Clone)]
struct Cfg { host: String, port: u16 }
let a = Cfg { host: "x".into(), port: 80 };
let b = Cfg { port: 443, ..a.clone() };
b.port  // 443

struct Meters(f64);
let m = Meters(1.5);
m.0  // 1.5

struct Marker;
let _m = Marker;  // unit-like

enum Msg { Quit, Move { x: i32, y: i32 }, Write(String) }
let m = Msg::Move { x: 1, y: 2 };
matches!(m, Msg::Move { .. })  // true

struct Counter { n: i32 }
impl Counter {
    fn inc(&mut self) { self.n += 1; }
    fn get(&self) -> i32 { self.n }
}
let mut c = Counter { n: 0 };
c.inc();
c.get()  // 1

struct Point { x: i32, y: i32 }
impl Point {
    fn origin() -> Self { Self { x: 0, y: 0 } }
}
Point::origin().x  // 0

let x: Option<i32> = Some(3);
x.unwrap_or(0)  // 3
None::<i32>.unwrap_or(0)  // 0

let r: Result<i32, &str> = Ok(1);
r.unwrap_or(-1)  // 1

enum Traffic { Red, Green }
impl Traffic {
    fn can_go(&self) -> bool { matches!(self, Traffic::Green) }
}
Traffic::Green.can_go()  // true

struct P { x: i32 }
P { x: 9 }.x  // 9

#[derive(Debug)]
struct P { x: i32 }
format!("{:?}", P { x: 1 })  // "P { x: 1 }"

#[derive(PartialEq)]
struct P { x: i32 }
P { x: 1 } == P { x: 1 }  // true

#[derive(Default)]
struct Cfg { port: u16 }
Cfg::default().port  // 0

struct UserId(u64);
let id = UserId(42);
id.0  // 42