Rust by Example

Overload

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

// `test!` will compare `$left` and `$right`

// in different ways depending on how you invoke it:

macro_rules! test {

// Arguments don't need to be separated by a comma.

// Any template can be used!

($left:expr; and $right:expr) => {

println!("{:?} and {:?} is {:?}",

stringify!($left),

stringify!($right),

$left && $right)

};

// ^ each arm must end with a semicolon.

($left:expr; or $right:expr) => {

println!("{:?} or {:?} is {:?}",

stringify!($left),

stringify!($right),

$left || $right)

};

}

fn main() {

test!(1i32 + 1 == 2i32; and 2i32 * 2 == 4i32);

test!(true; or false);

}

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