feat: 🎸 added solution for quiz3

exercises/quiz3.rs

@@ -14,18 +14,38 @@
 
 // Execute `rustlings hint quiz3` or use the `hint` watch subcommand for a hint.
 
-// I AM NOT DONE
+pub trait Grade {
+    fn to_string(&self) -> String;
+}
 
-pub struct ReportCard {
-    pub grade: f32,
+pub struct StrGrade(String);
+pub struct NumGrade(f32);
+
+impl Grade for StrGrade {
+    fn to_string(&self) -> String {
+        self.0.to_string()
+    }
+}
+impl Grade for NumGrade {
+    fn to_string(&self) -> String {
+        self.0.to_string()
+    }
+}
+
+pub struct ReportCard<G: Grade> {
+    pub grade: G,
     pub student_name: String,
     pub student_age: u8,
 }
 
-impl ReportCard {
+impl<G: Grade> ReportCard<G> {
     pub fn print(&self) -> String {
-        format!("{} ({}) - achieved a grade of {}",
-            &self.student_name, &self.student_age, &self.grade)
+        format!(
+            "{} ({}) - achieved a grade of {}",
+            &self.student_name,
+            &self.student_age,
+            &self.grade.to_string()
+        )
     }
 }
 
@@ -36,7 +56,7 @@ mod tests {
     #[test]
     fn generate_numeric_report_card() {
         let report_card = ReportCard {
-            grade: 2.1,
+            grade: NumGrade(2.1),
             student_name: "Tom Wriggle".to_string(),
             student_age: 12,
         };
@@ -50,7 +70,7 @@ mod tests {
     fn generate_alphabetic_report_card() {
         // TODO: Make sure to change the grade here after you finish the exercise.
         let report_card = ReportCard {
-            grade: 2.1,
+            grade: StrGrade(String::from("A+")),
             student_name: "Gary Plotter".to_string(),
             student_age: 11,
         };