Rust Systems

Ownership and Borrowing

fn process_data(data: &[u8]) -> Vec<u8> {
    data.iter().map(|b| b.wrapping_add(1)).collect()
}

fn modify_in_place(data: &mut Vec<u8>) {
    data.retain(|b| *b != 0);
    data.sort_unstable();
}

fn take_ownership(data: Vec<u8>) -> Vec<u8> {
    let mut result = data;
    result.push(0xFF);
    result
}

fn main() {
    let data = vec![1, 2, 3, 0, 4];
    let processed = process_data(&data);     // borrow: data still usable
    let mut owned = take_ownership(data);     // move: data no longer usable
    modify_in_place(&mut owned);              // mutable borrow
}

Prefer borrowing (&T, &mut T) over ownership transfer. Use Clone only when necessary.

Error Handling

use thiserror::Error;

#[derive(Error, Debug)]
pub enum AppError {
    #[error("database error: {0}")]
    Database(#[from] sqlx::Error),

    #[error("not found: {resource} with id {id}")]
    NotFound { resource: &'static str, id: String },

    #[error("validation failed: {0}")]
    Validation(String),
}

type Result<T> = std::result::Result<T, AppError>;

async fn get_user(pool: &PgPool, id: &str) -> Result<User> {
    sqlx::query_as::<_, User>("SELECT * FROM users WHERE id = $1")
        .bind(id)
        .fetch_optional(pool)
        .await?
        .ok_or_else(|| AppError::NotFound {
            resource: "User",
            id: id.to_string(),
        })
}

Use thiserror for library errors, anyhow for application-level errors. Avoid .unwrap() in production code.

Traits and Generics

trait Repository {
    type Item;
    type Error;

    async fn find_by_id(&self, id: &str) -> std::result::Result<Option<Self::Item>, Self::Error>;
    async fn save(&self, item: &Self::Item) -> std::result::Result<(), Self::Error>;
}

struct PgUserRepo {
    pool: PgPool,
}

impl Repository for PgUserRepo {
    type Item = User;
    type Error = AppError;