Value binding

Bind matched values with pattern variables.

Binding values

Patterns can take values apart (destructure) and bind them to variables. Tuples, structs and enums are unpacked the same way:

let nokta = (3, 0);
match nokta {
    (0, 0) => println!("merkez"),
    (x, 0) => println!("x ekseni {x}"),
    (0, y) => println!("y ekseni {y}"),
    (x, y) => println!("{x},{y}"),
}

Literal parts narrow the match, variable parts capture the value.

Struct destructuring and @

Struct fields are unpacked by name; .. ignores the remaining fields. name @ pattern both checks the pattern and binds the value:

struct Oyuncu { ad: String, puan: u32 }

let o = Oyuncu { ad: String::from("Ece"), puan: 87 };
match o {
    Oyuncu { puan: p @ 80..=100, .. } => println!("usta: {p}"),
    Oyuncu { ad, .. } => println!("{ad} çalışmalı"),
}

Exercise Classify points

Loop over the array [(0, 0), (3, 0), (0, 5), (2, 2)] and classify each point with match: merkez, x ekseni N, y ekseni N or x,y. Print each result on its own line.

Show example solution

fn main() {
    let noktalar = [(0, 0), (3, 0), (0, 5), (2, 2)];
    for n in noktalar {
        match n {
            (0, 0) => println!("merkez"),
            (x, 0) => println!("x ekseni {}", x),
            (0, y) => println!("y ekseni {}", y),
            (x, y) => println!("{},{}", x, y),
        }
    }
}

Test yourself

Which arm does <code>match (0, 7) { (x, 0) => .., (0, y) => .., _ => .. }</code> take?
- (0, y) with y = 7
- (x, 0) with x = 0
- _
- None
Show answer

(0, y) with y = 7 — The first arm doesn't fit because the second element isn't 0; the second arm fits because the first element is 0.

Bind the range

match yas {
    n ____ 0..=17 => println!("{n}: çocuk"),
    n => println!("{n}: yetişkin"),
}

Show answer

match yas {
    n @ 0..=17 => println!("{n}: çocuk"),
    n => println!("{n}: yetişkin"),
}

Pattern and meaning

(x, 0)

Second element 0, x is bound
Oyuncu { ad, .. }

Only the ad field
p @ 80..=100

Range + binding
(_, y)

The first is ignored

Next lesson: if let

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