// Variables
let x = 5;           // Immutable
let mut y = 10;      // Mutable

// Functions
fn add(a: i32, b: i32) -> i32 {
    a + b  // No semicolon = return
}

// Structs
struct User {
    name: String,
    age: u32,
}

// Enums
enum Status {
    Active,
    Inactive,
    Pending(String),
}

// Ownership
let s1 = String::from("hello");
let s2 = s1;  // s1 moved to s2

// Borrowing
fn print(s: &String) {
    println!("{}", s);
}

// Mutable borrow
fn append(s: &mut String) {
    s.push_str(" world");
}

use axum::{routing::get, Router, Json};
use serde::Serialize;

#[derive(Serialize)]
struct User { name: String }

async fn get_user() -> Json<User> {
    Json(User { name: "John".into() })
}

#[tokio::main]
async fn main() {
    let app = Router::new()
        .route("/user", get(get_user));
    
    axum::serve(listener, app).await.unwrap();
}

use tokio;

#[tokio::main]
async fn main() {
    let result = fetch_data().await;
}

async fn fetch_data() -> String {
    tokio::time::sleep(Duration::from_secs(1)).await;
    "data".to_string()
}

use anyhow::Result;
use thiserror::Error;

#[derive(Error, Debug)]
enum AppError {
    #[error("Not found: {0}")]
    NotFound(String),
}

fn find_user(id: &str) -> Result<User> {
    // Returns Result with anyhow
    Ok(user)
}