Rust High Performance

Macro variants

As you can see, it's not as complicated as you might think. As I wrote, you can have almost any pattern to the left of the macro_rules!{} side. Not only that, you can also have multiple patterns, as if it were a match statement, so that if one of them matches, it will be the one expanded. Let's see how this works by creating a macro which, depending on how we call it, will add one or two to the given integer:

macro_rules! add {    {one to $input:expr} => ($input + 1);    {two to $input:expr} => ($input + 2);}fn main() {    println!("Add one: {}", add!(one to 25/5));    println!("Add two: {}", add!(two to 25/5));}

You can see a couple of clear changes to the macro. First, we swapped braces for parentheses and parentheses for braces in the ...