Modules

Additional Resources

• Rust's Module System Explained!

Exercises

Visibility

// Something's missing. Fix the code so that it compiles.

mod sausage_factory {
    // Don't let anybody outside of this module see this!
    fn get_secret_recipe() -> String {
        String::from("Ginger")
    }

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

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

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();
}

Bringing item into scope

// Complete the following code by addressing the TODO.

// TODO: Complete this use statement
use ???

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!"),
    }
}

use std::time::SystemTime;

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

Multi-file projects 1

// Complete the code by bringing the required items into scope.

mod days {
    pub enum WeekDay {
        Sunday,
        Monday,
        Tuesday,
        Wednesday,
        Thursday,
        Friday,
        Saturday,
    }
    
    pub fn is_holiday(day: &WeekDay) -> bool {
        match day {
            WeekDay::Sunday | WeekDay::Saturday => true,
            _ => false,
        }
    }
}

fn main() {
    let today = WeekDay::Friday;
    if is_holiday(&today) {
        println!("I can go out!");
    } else {
        println!("I have to work today!");
    }
}

use days::{WeekDay, is_holiday};

mod days {
  pub enum WeekDay {
      Sunday,
      Monday,
      Tuesday,
      Wednesday,
      Thursday,
      Friday,
      Saturday,
  }
  
  pub fn is_holiday(day: &WeekDay) -> bool {
      match day {
          WeekDay::Sunday | WeekDay::Saturday => true,
          _ => false,
      }
  }
}

fn main() {
  let today = WeekDay::Friday;
  if is_holiday(&today) {
      println!("I can go out!");
  } else {
      println!("I have to work today!");
  }
}

Multi-file projects 2

// Complete the code by use declarations above main.

mod student {
    pub mod operations {
        use super::Student; // using super to refer to parent module

        pub fn assign_grade(student: &mut Student) {
            if student.marks >= 80 {
                student.grade = 'A';
            } else if student.marks >= 60 {
                student.grade = 'B';
            } else {
                student.grade = 'C';
            }
        }

    }

pub struct Student {
    pub name: String, // struct fields can also be made public
    pub marks: u8,
    pub grade: char,
}

impl Student {
    // make methods/associated functions public in order to access from outside the module
    pub fn new(name: &str, marks: u8) -> Self {
        Self {
            name: name.to_string(),
            marks,
            grade: 'X',
        }
    }
}

}

fn main() {
    let mut student = Student::new("Alice", 75);
    assign_grade(&mut student);
    println!("{} got {} grade", student.name, student.grade);
}

mod student {
  pub mod operations {
      use super::Student;

      pub fn assign_grade(student: &mut Student) {
          if student.marks >= 80 {
              student.grade = 'A';
          } else if student.marks >= 60 {
              student.grade = 'B';
          } else {
              student.grade = 'C';
          }
      }

  }

pub struct Student {
  pub name: String,
  pub marks: u8,
  pub grade: char,
}

impl Student {
  pub fn new(name: &str, marks: u8) -> Self {
      Self {
          name: name.to_string(),
          marks,
          grade: 'X',
      }
  }
}

}

use student::{Student, operations::assign_grade};

fn main() {
  let mut student = Student::new("Alice", 75);
  assign_grade(&mut student);
  println!("{} got {} grade", student.name, student.grade);
}

Re-exporting

// Make the code compile by addressing the TODO.

mod delicious_snacks {
    // TODO: Fix these use statements
    use self::fruits::PEAR as ???
    use self::veggies::CUCUMBER as ???

    mod fruits { // 'static just implies that reference will be valid throughout program execution
        pub const PEAR: &'static str = "Pear";
        pub const APPLE: &'static str = "Apple";
    }

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

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

// Make the code compile by addressing the TODO.

mod delicious_snacks {
  pub use self::fruits::PEAR as fruit;
  pub use self::veggies::CUCUMBER as veggie;

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

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

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