Rust for C-Programmers

21.18 Example of Nested Pattern Matching

Patterns can be deeply nested, matching multiple levels at once:

enum Connection {
    Tcp { ip: (u8, u8, u8, u8), port: u16 },
    Udp { ip: (u8, u8, u8, u8), port: u16 },
    Unix { path: String },
}

fn main() {
    let conn = Connection::Tcp { ip: (127, 0, 0, 1), port: 8080 };

    match conn {
        Connection::Tcp { ip: (127, 0, 0, 1), port } => {
            println!("Localhost with port {}", port);
        }
        Connection::Tcp { ip, port } => {
            println!("TCP {}.{}.{}.{}:{}", ip.0, ip.1, ip.2, ip.3, port);
        }
        Connection::Udp { ip, port } => {
            println!("UDP {}.{}.{}.{}:{}", ip.0, ip.1, ip.2, ip.3, port);
        }
        Connection::Unix { path } => {
            println!("Unix socket at {}", path);
        }
    }
}

Here, Connection::Tcp { ip: (127, 0, 0, 1), port } is a nested pattern that checks for a specific IP tuple while still binding port.