Overload

Macros can be overloaded to accept different combinations of arguments. In that regard, macro_rules! can work similarly to a match block:

1. // `test!` will compare `$left` and `$right`
2. // in different ways depending on how you invoke it:
3. macro_rules! test {
4. // Arguments don't need to be separated by a comma.
5. // Any template can be used!
6. ($left:expr; and $right:expr) => (
7. println!("{:?} and {:?} is {:?}",
8. stringify!($left),
9. stringify!($right),
10. $left && $right)
11. );
12. // ^ each arm must end with a semicolon.
13. ($left:expr; or $right:expr) => (
14. println!("{:?} or {:?} is {:?}",
15. stringify!($left),
16. stringify!($right),
17. $left || $right)
18. );
19. }

21. fn main() {
22. test!(1i32 + 1 == 2i32; and 2i32 * 2 == 4i32);
23. test!(true; or false);
24. }