Rust for C-Programmers

21.4 Plain Variable Assignment as a Pattern

Every let x = something; statement in Rust is technically a pattern match where x is the pattern. This can be more elaborate:

fn main() {
    let (width, height) = (20, 10);
    println!("Width = {}, Height = {}", width, height);
}

Here, (width, height) is an irrefutable tuple pattern that binds each element to a separate variable. A mismatch is impossible: (20, 10) always matches (width, height). Attempting a refutable pattern—something that might fail—would be invalid in a regular let statement.