函数使用fn关键字声明。 其参数的数据类型注解，就像变量，并且如果该函数返回一个值，返回类型必须箭头后指定 ->.
在函数的最终表达式将被用作返回值。或者， return语句可用于早期从函数内返回一个值，即使从内循环或 if 语句
让我们改写FizzBuzz使用函数！
| // 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); |
| } |
| } |
