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 ifs.
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);
}
}