Functions

Functions group reusable logic. You declare them with fn, give each parameter a type, and optionally specify a return type.

Defining a function

fn greet() {
    println!("Hello from a function!");
}

fn main() {
    greet();
}

Typed parameters

Every parameter must have an explicit type.

fn print_sum(a: i32, b: i32) {
    println!("Sum: {}", a + b);
}

fn main() {
    print_sum(4, 7); // Sum: 11
}

Return values

Use -> to declare the return type. The last expression, written without a semicolon, becomes the return value.

fn square(n: i32) -> i32 {
    n * n // no semicolon: this is the returned value
}

fn main() {
    let result = square(5);
    println!("{}", result); // 25
}

Early return

You can also return early with the return keyword.

fn abs(n: i32) -> i32 {
    if n < 0 {
        return -n;
    }
    n
}

Remember: adding a semicolon to the final expression turns it into a statement, which returns the unit type () instead of your value.