Optional Parameters in Rust, different methods

main.rs

#[allow(dead_code)]
fn f1(a: i32) -> i32 {
    a    
}
#[allow(dead_code)]
fn f2(a: i32, b: i32) -> i32 {
    a+b
}

#[allow(dead_code)]
fn f3(a: i32, b: i32, c: i32) -> i32 {
    a+b+c
}
macro_rules! sum3{
    ($x: expr) => {f1($x)}; //call function f1 when there's one variable
    ($x: expr, $y: expr) => {f2($x, $y)}; //call f2 when there are two
    ($x: expr, $y: expr, $z: expr) => {f3($x, $y, $z)}; //call f2 when there are two

}

fn add(a: i32, b: impl Into<Option<i32>>) -> i32 { 
    a + b.into().unwrap_or(0) 
}

macro_rules! sum {
    ($h:expr) => ($h);
    ($h:expr, $($t:expr),*) =>
        ($h + sum!($($t),*));
}

fn main() {
    dbg!(add(100,1));
    dbg!(sum3!(100,200));
    dbg!(sum!(100,200, 10, 20, "2"));
}