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Pattern Matching in Rust

Patterns destructure data and control flow via match, if let, and while let.

Destructuring

Unpack tuples, structs, and enums.

let tup = (1, 2);
let (a, b) = tup;

struct Point { x: i32, y: i32 }
let p = Point { x: 1, y: 2 };
let Point { x, y: y2 } = p;

match with guards

let v = Some(10);
match v {
    Some(n) if n > 5 => println!("gt5"),
    Some(_) => println!("some"),
    None => println!("none"),
}

Binding and @ patterns

let x = 7;
match x {
    n @ 1..=9 => println!("digit {n}"),
    _ => {}
}

Or-patterns and ranges

let c = 'a';
match c {
    'a' | 'e' | 'i' | 'o' | 'u' => println!("vowel"),
    '0'..='9' => println!("digit"),
    _ => {}
}

if let / while let

Convenience when matching a single pattern.

if let Some(n) = v { println!("{n}") }

let mut it = (0..3).into_iter();
while let Some(n) = it.next() { println!("{n}") }

Ref and mut in patterns

Borrow or mutably borrow while matching.

let mut s = String::from("hi");
let r = &mut s;
match r {
    ref mut m => m.push('!'),
}

Summary

  • Use patterns to destructure and inspect values concisely
  • Add guards, use bindings, and combine patterns for readable matches
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