Summary - Pattern matching

Combine match, if let and the _ wildcard to build a command interpreter.

Pattern matching summary

match is exhaustive and runs the first arm that fits. Patterns: literals, |, ..= ranges, tuple/struct/enum destructuring, @ binding, _ and ... Use if let for a single pattern, while let for loops, let-else for early exit and matches! for a bool. Arms can also have a guard: x if x < 0 => ...

Match guards

For conditions that a pattern alone can't express, an if is added to the arm:

fn sinif(n: i32) -> &'static str {
    match n {
        x if x < 0 => "negatif",
        0 => "sıfır",
        x if x % 2 == 0 => "çift",
        _ => "tek",
    }
}

A guard applies to all patterns joined with |: 1 | 2 if kosul → (1 or 2) and the condition.

Exercise Number class

Write the function fn sinif(n: i32) -> &'static str above with match guards. Print the results for -3, 0, 4 and 7 on one line separated by spaces.

Show example solution

fn sinif(n: i32) -> &'static str {
    match n {
        x if x < 0 => "negatif",
        0 => "sıfır",
        x if x % 2 == 0 => "çift",
        _ => "tek",
    }
}

fn main() {
    println!("{} {} {} {}", sinif(-3), sinif(0), sinif(4), sinif(7));
}

Test yourself

What is needed for exhaustiveness when using guarded arms?
- Usually an unguarded final arm (like _)
- Nothing; the compiler solves the conditions
- A guard on every arm
- An else block
Show answer

Usually an unguarded final arm (like _) — The compiler doesn't evaluate guard expressions, so an unguarded arm must cover the remaining cases.

Add a guard

match n {
    x ____ x < 0 => "negatif",
    _ => "pozitif ya da sıfır",
}

Show answer

match n {
    x if x < 0 => "negatif",
    _ => "pozitif ya da sıfır",
}

sinif() input and result

-3

negatif
0

sıfır
4

çift
7

tek

Next lesson: Task model

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