Macros

Macros are expanded into Rust code during compilation, and can take a variable number of arguments. They are distinguished by a ! at the end. The Rust standard library includes an assortment of useful macros.

• println!(format, ..) prints a line to standard output, applying formatting described in std::fmt.
• format!(format, ..) works just like println! but returns the result as a string.
• dbg!(expression) logs the value of the expression and returns it.
• todo!() marks a bit of code as not-yet-implemented. If executed, it will panic.
• unreachable!() marks a bit of code as unreachable. If executed, it will panic.

fn factorial(n: u32) -> u32 {
    let mut product = 1;
    for i in 1..=n {
        product *= dbg!(i);
    }
    product
}

fn fizzbuzz(n: u32) -> u32 {
    todo!()
}

fn main() {
    let n = 4;
    println!("{n}! = {}", factorial(n));
}