Option<T> and Result<T,E>: encoding absence and failure in the type system

Developers unfamiliar with Rust try to use null pointers or panic on errors instead of using Option and Result, missing Rust's key safety guarantee.

Use Option<T> for values that may be absent, and Result<T, E> for operations that may fail:

// Option: Some(value) or None
fn find_user(id: u32) -> Option<String> {
    if id == 1 { Some(String::from("Alice")) } else { None }
}

match find_user(1) {
    Some(name) => println!("Found: {}", name),
    None       => println!("Not found"),
}

// Chaining with map, and_then, unwrap_or
let name = find_user(2).unwrap_or_else(|| String::from("Guest"));

// Result: Ok(value) or Err(error)
fn parse_port(s: &str) -> Result<u16, std::num::ParseIntError> {
    s.parse::<u16>()
}

match parse_port("8080") {
    Ok(port) => println!("Port: {}", port),
    Err(e)   => eprintln!("Bad port: {}", e),
}

Option and Result make failure states explicit and impossible to ignore. The compiler forces you to handle both branches, eliminating null pointer exceptions and unhandled errors at compile time.