rust-patterns

Rust Patterns

Project Structure

my-app/
├── Cargo.toml
├── src/
│   ├── main.rs           # Binary entry point
│   ├── lib.rs            # Library root (re-exports)
│   ├── error.rs          # Crate-level error types
│   ├── api/
│   │   ├── mod.rs
│   │   └── handlers.rs
│   └── domain/
│       ├── mod.rs
│       └── service.rs
├── tests/                # Integration tests (separate crate)
│   └── api_test.rs
├── benches/              # criterion benchmarks
│   └── throughput.rs
└── examples/
    └── demo.rs

Workspace layout for multi-crate projects:

# Cargo.toml (workspace root)
[workspace]
resolver = "2"
members = ["crates/core", "crates/api", "crates/cli"]

[workspace.dependencies]
serde = { version = "1", features = ["derive"] }
tokio = { version = "1", features = ["full"] }

---

Idioms / Code Style

Ownership and Borrowing

// Borrow when you only need to read
fn print_name(name: &str) { println!("{name}"); }

// Take ownership when storing or consuming the value
fn register_user(name: String) -> User {
    User { name, id: Uuid::new_v4() }
}

Lifetimes

// Annotate only when the compiler cannot infer
struct Parser<'input> {
    source: &'input str,
    pos: usize,
}

impl<'input> Parser<'input> {
    fn next_token(&mut self) -> Option<&'input str> {
        let start = self.pos;
        // ... advance self.pos ...
        Some(&self.source[start..self.pos])
    }
}

Trait-Based Design

trait Repository {
    fn find_by_id(&self, id: Uuid) -> Result<Option<User>, DbError>;
    fn save(&self, user: &User) -> Result<(), DbError>;
}

// Accept generics for testability
fn create_user(repo: &impl Repository, name: String) -> Result<User, AppError> {
    let user = User::new(name);
    repo.save(&user)?;
    Ok(user)
}

Iterators, Pattern Matching, Newtype

// Iterator chains over manual loops
let active: Vec<&str> = users.iter()
    .filter(|u| u.is_active)
    .map(|u| u.email.as_str())
    .collect();

// Exhaustive matching
match command {
    Command::Start { port } => start_server(port),
    Command::Stop => shutdown(),
}

// let-else for early exit (Rust 1.65+)
let Some(cfg) = load_config() else { return Ok(Config::default()); };

// Newtype to prevent primitive misuse
struct UserId(Uuid);
struct Email(String);

impl Email {
    fn new(raw: &str) -> Result<Self, ValidationError> {
        if raw.contains('@') { Ok(Self(raw.to_lowercase())) }
        else { Err(ValidationError::InvalidEmail) }
    }
}