Quiz 3

// This quiz tests:
// - Generics
// - Traits
//
// An imaginary magical school has a new report card generation system written
// in Rust! Currently, the system only supports creating report cards where the
// student's grade is represented numerically (e.g. 1.0 -> 5.5). However, the
// school also issues alphabetical grades (A+ -> F-) and needs to be able to
// print both types of report card!
//
// Make the necessary code changes in the struct `ReportCard` and the impl
// block to support alphabetical report cards in addition to numerical ones.

// TODO: Adjust the struct as described above.
struct ReportCard {
    grade: f32,
    student_name: String,
    student_age: u8,
}

// TODO: Adjust the impl block as described above.
impl ReportCard {
    fn print(&self) -> String {
        format!(
            "{} ({}) - achieved a grade of {}",
            &self.student_name, &self.student_age, &self.grade,
        )
    }
}

fn main() {
    // You can optionally experiment here.
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn generate_numeric_report_card() {
        let report_card = ReportCard {
            grade: 2.1,
            student_name: "Tom Wriggle".to_string(),
            student_age: 12,
        };
        assert_eq!(
            report_card.print(),
            "Tom Wriggle (12) - achieved a grade of 2.1",
        );
    }

    #[test]
    fn generate_alphabetic_report_card() {
        let report_card = ReportCard {
            grade: "A+",
            student_name: "Gary Plotter".to_string(),
            student_age: 11,
        };
        assert_eq!(
            report_card.print(),
            "Gary Plotter (11) - achieved a grade of A+",
        );
    }
}

• In this quiz we are tasked to adjust ReportCard and its implementation to accept both text grade and float grade.

• We can use generics for this.

• First we need to change the ReportCard struct so it will accept generic types for grade field like this:

  struct ReportCard<T> {
      grade: T,
      student_name: String,
      student_age: u8,
  }

• Then we adjust the implementation to accept generics as well like this:

  impl<T> ReportCard<T> {
      fn print(&self) -> String {
          format!(
              "{} ({}) - achieved a grade of {}",
              &self.student_name, &self.student_age, &self.grade,
          )
      }
  }

• But we still have some error below when compiling.

  error[E0277]: `T` doesn't implement `std::fmt::Display`

• This is because format! need certain traits.

• So we can add the std::fmt::Display trait into our impl syntax like this:

  impl<T: std::fmt::Display> ReportCard<T> {
      fn print(&self) -> String {
          format!(
              "{} ({}) - achieved a grade of {}",
              &self.student_name, &self.student_age, &self.grade,
          )
      }
  }

• In this quiz Rust compiler is very useful, it can suggest what trait should be added in the impl syntax.

References

• Traits
• Generic Data Types
• Bounds