Pattern Matching

The match expression provides precise condition checking and data unpacking (destructuring). The first matching pattern block is executed.

IMPORTANT

Exhaustiveness Checking The Zephyr compiler verifies that a match expression covers every possible case for the target enum or range. A missing case is a compile-time error. Use the wildcard _ to explicitly handle remaining cases.

Literals and Ranges

Match against numeric or string literals, or use the ..= range operator:

let score = 85;
match score {
    90..=100 => print("A"),
    80..=89  => print("B"),
    70..=79  => print("C"),
    _        => print("F"),
}

Destructuring

Extract payload data from enums, structs, or tuples directly into local variables within the match scope.

Enum Patterns

enum Message {
    Quit,
    Move(int, int),
    Write(string),
}

let msg = Message::Move(10, 20);

match msg {
    Message::Quit        => print("quit"),
    Message::Move(x, y)  => print(f"move to {x},{y}"),
    Message::Write(text) => print(text),
}

Struct Patterns

Selectively match specific fields (x: 0) while extracting others (y):

struct Point { x: int, y: int }
let p = Point { x: 0, y: 5 };

match p {
    Point { x: 0, y } => print(f"on y-axis at {y}"),
    Point { x, y: 0 } => print(f"on x-axis at {x}"),
    Point { x, y }    => print(f"at ({x}, {y})"),
}

Tuple and Array Patterns

// Tuple destructuring with value matching
let pair = (true, 42);
match pair {
    (true, n)  => print(f"yes: {n}"),
    (false, n) => print(f"no: {n}"),
}

// Array pattern matching
match [1, 2, 3] {
    [1, x, y] => print(f"starts with 1, then {x} and {y}"),
    _         => print("something else"),
}

Guard Conditions

Add an if expression after a pattern to impose an additional runtime condition:

let n = 7;
match n {
    x if x % 2 == 0 => print(f"{x} is even"),
    x                => print(f"{x} is odd"),
}

Result<T> Error Handling

Because Zephyr does not use exceptions (throw), match is the idiomatic way to handle success/failure:

match divide(10, 0) {
    Ok(v)    => print(f"success: {v}"),
    Err(msg) => print(f"error: {msg}"),
}