Functions - Rust By Example
Description: A description

# Functions

Functions are declared using the `fn` keyword. Its arguments are type annotated, just like variables, and, if the function returns a value, the return type must be specified after an arrow `->`.

The final expression in the function will be used as return value. Alternatively, the `return` statement can be used to return a value earlier from within the function, even from inside loops or `if` statements.

Let's rewrite FizzBuzz using functions!

    // Unlike C/C++, there's no restriction on the order of function definitions
    fn main() {
        // We can use this function here, and define it somewhere later
        fizzbuzz_to(100);
    }

    // Function that returns a boolean value
    fn is_divisible_by(lhs: u32, rhs: u32) -> bool {
        // Corner case, early return
        if rhs == 0 {
            return false;
        }

        // This is an expression, the `return` keyword is not necessary here
        lhs % rhs == 0
    }

    // Functions that "don't" return a value, actually return the unit type `()`
    fn fizzbuzz(n: u32) -> () {
        if is_divisible_by(n, 15) {
            println!("fizzbuzz");
        } else if is_divisible_by(n, 3) {
            println!("fizz");
        } else if is_divisible_by(n, 5) {
            println!("buzz");
        } else {
            println!("{}", n);
        }
    }

    // When a function returns `()`, the return type can be omitted from the
    // signature
    fn fizzbuzz_to(n: u32) {
        for n in 1..n + 1 {
            fizzbuzz(n);
        }
    }