Critical Patterns

Error Handling (REQUIRED)

// ✅ ALWAYS: Use Result with ? operator fn read_config(path: &str) -> Result<Config, ConfigError> { let content = std::fs::read_to_string(path)?; let config: Config = serde_json::from_str(&content)?; Ok(config) }

// ❌ NEVER: Use unwrap in production let config = std::fs::read_to_string(path).unwrap();

Ownership Patterns (REQUIRED)

// ✅ ALWAYS: Prefer borrowing over ownership transfer fn process(data: &[u8]) -> Result<(), Error> { ... }

// ✅ Use Clone only when necessary fn take_ownership(data: Vec<u8>) -> Vec<u8> { ... }

// ❌ NEVER: Unnecessary cloning process(data.clone()); // If borrow works, use it

Option Handling (REQUIRED)

// ✅ ALWAYS: Pattern match or use combinators let name = user.name.as_ref().unwrap_or(&default_name);

// ✅ Use if let for single variant if let Some(name) = user.name { println!("Hello, {}", name); }

// ❌ NEVER: Blind unwrap let name = user.name.unwrap();

Decision Tree

Need to modify data? → Use &mut reference Need to read data? → Use & reference Need to transfer? → Move ownership Need cleanup? → Implement Drop trait Need async? → Use tokio or async-std Need error context? → Use anyhow or thiserror

Code Examples

Struct with Lifetimes

struct Parser<'a> { input: &'a str, position: usize, }

impl<'a> Parser<'a> { fn new(input: &'a str) -> Self { Self { input, position: 0 } } }

Async with Tokio

use tokio;

#[tokio::main] async fn main() -> Result<(), Box<dyn std::error::Error>> { let response = reqwest::get("https://api.example.com/data") .await? .json::<Response>() .await?;

Ok(())

}

Commands

cargo new myapp # Create new project cargo build --release # Build optimized cargo run # Build and run cargo test # Run tests cargo clippy # Linting cargo fmt # Format code

Resources

• Ownership & Borrowing: ownership-borrowing.md

• Async Programming: async-programming.md

• Best Practices: best-practices.md