Modules

• Use pub keyword to make items public.

• Use use keyword to brings a path into scope.

• Use as keyword to make alias for a path that brought to scope by using use.

• A path can take two forms:

  • An absolute path is the full path starting from a crate root; for code from an external crate, the absolute path begins with the crate name, and for code from the current crate, it starts with the literal crate.

  • A relative path starts from the current module and uses self, super, or an identifier in the current module.

• References:

  • The Module System

  • Defining Modules to Control Scope and Privacy

  • Bringing Paths into Scope with the use Keyword

modules1.rs

// TODO: Fix the compiler error about calling a private function.
mod sausage_factory {
    // Don't let anybody outside of this module see this!
    fn get_secret_recipe() -> String {
        String::from("Ginger")
    }

    pub fn make_sausage() {
        get_secret_recipe();
        println!("sausage!");
    }
}

fn main() {
    sausage_factory::make_sausage();
}

• This exercise is simple we just need to make the make_sausage function accessible from main function but not the get_secret_recipe function.

• We can do this by adding pub before fn make_sausage().

modules2.rs

// You can bring module paths into scopes and provide new names for them with
// the `use` and `as` keywords.

mod delicious_snacks {
    // TODO: Add the following two `use` statements after fixing them.
    pub use self::fruits::PEAR as fruit; // as fruit and add pub
    pub use self::veggies::CUCUMBER as veggie; // as veggie and add pub

    mod fruits {
        pub const PEAR: &str = "Pear";
        pub const APPLE: &str = "Apple";
    }

    mod veggies {
        pub const CUCUMBER: &str = "Cucumber";
        pub const CARROT: &str = "Carrot";
    }
}

fn main() {
    println!(
        "favorite snacks: {} and {}",
        delicious_snacks::fruit,
        delicious_snacks::veggie,
    );
}

• In this exercise the TODO stated that we need to complete the use syntax below:

  use self::fruits::PEAR as ???;
  use self::veggies::CUCUMBER as ???;

• So we can conclude that we need to re-export the constant PEAR as fruit and CUCUMBER as veggie.

• Don forget to add pub so it's accessible in main function.

modules3.rs

// You can use the `use` keyword to bring module paths from modules from
// anywhere and especially from the standard library into your scope.

// TODO: Bring `SystemTime` and `UNIX_EPOCH` from the `std::time` module into
// your scope. Bonus style points if you can do it with one line!
// use ???;

use std::time::SystemTime;
use std::time::UNIX_EPOCH;

fn main() {
    match SystemTime::now().duration_since(UNIX_EPOCH) {
        Ok(n) => println!("1970-01-01 00:00:00 UTC was {} seconds ago!", n.as_secs()),
        Err(_) => panic!("SystemTime before UNIX EPOCH!"),
    }
}

• In this exercise we need to bring SystemTime and UNIX_EPOCH into main scope.

• We can do this by using use like below:

  use std::time::SystemTime;
  use std::time::UNIX_EPOCH;