Using mod.rs

main.rs

mod calc;
mod foo;

fn main() {
  assert!(foo::bar());
  assert_eq!(2, calc::mul::mul(2, calc::mul::MUL_IDENTITY));
  println!("{}", calc::hello());
}

mod.rs

pub mod mul;
mod strings;	// Hidden to the outside world

pub fn hello() -> &'static str {
  strings::HELLO
}

mul.rs

pub const MUL_IDENTITY: usize = 1;

pub fn mul<T: std::ops::Mul<Output = T>>(left: T, right: T) -> T {
  left * right
}

strings.rs

pub const HELLO: &'static str = "Hello Math World!";