> For the complete documentation index, see [llms.txt](https://bagus-cahyono.gitbook.io/programming-notes/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://bagus-cahyono.gitbook.io/programming-notes/rust/rustlings_exercise/quiz_3.md).

# Quiz 3

```rust
// 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:

  ```rust
  struct ReportCard<T> {
      grade: T,
      student_name: String,
      student_age: u8,
  }
  ```
* Then we adjust the implementation to accept generics as well like this:

  ```rust
  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:

  ```rust
  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](https://doc.rust-lang.org/book/ch10-02-traits.html)
* [Generic Data Types](https://doc.rust-lang.org/book/ch10-01-syntax.html)
* [Bounds](https://doc.rust-lang.org/rust-by-example/generics/bounds.html)