Attribute Macro extend_parameter_list 

#[extend_parameter_list]

Turns something like:

#[mod_template::extend_parameter_list(.., mut input: i32, output: &mut i32)]
fn abs() {
    input = input.abs();
    *output = input;
}

into:

fn abs(mut input: i32, output: &mut i32) {
    input = input.abs();
    *output = input;
}

See mod_template::extend_parameter_list.