Rust for C-Programmers

21.5 match Expressions

The match expression is Rust’s primary tool for complex pattern matching. It evaluates an expression and executes the code associated with the first matching pattern arm.

match VALUE_EXPRESSION {
    PATTERN_1 => CODE_BLOCK_1,
    PATTERN_2 => CODE_BLOCK_2,
    // ...
    PATTERN_N => CODE_BLOCK_N,
}

21.5.1 Example: Matching Option<T>

Handling optional values is a classic use case:

fn check_option(opt: Option<&str>) {
    match opt {
        Some(message) => {
            println!("Received message: {}", message);
        }
        None => {
            println!("No message received.");
        }
    }
}

fn main() {
    check_option(Some("Processing Data")); // Output: Received message: Processing Data
    check_option(None);                   // Output: No message received.
}

The compiler ensures all possibilities (Some and None) are handled, guaranteeing exhaustiveness.