finish until lifetimes

.rustlings-state.txt

@@ -1,6 +1,6 @@
 DON'T EDIT THIS FILE!
 
-quiz3
+tests1
 
 intro1
 intro2
@@ -64,4 +64,8 @@ traits1
 traits2
 traits3
 traits4
-traits5
+traits5
+quiz3
+lifetimes1
+lifetimes2
+lifetimes3

exercises/16_lifetimes/lifetimes1.rs

@@ -4,7 +4,7 @@
 // not own their own data. What if their owner goes out of scope?
 
 // TODO: Fix the compiler error by updating the function signature.
-fn longest(x: &str, y: &str) -> &str {
+fn longest<'a>(x: &'a str, y: &'a str) -> &'a str {
     if x.len() > y.len() {
         x
     } else {

exercises/16_lifetimes/lifetimes2.rs

@@ -15,6 +15,6 @@ fn main() {
     {
         let string2 = String::from("xyz");
         result = longest(&string1, &string2);
+        println!("The longest string is '{result}'");
     }
-    println!("The longest string is '{result}'");
 }

exercises/16_lifetimes/lifetimes3.rs

@@ -1,11 +1,12 @@
 // Lifetimes are also needed when structs hold references.
 
 // TODO: Fix the compiler errors about the struct.
-struct Book {
+struct Book<'a> {
-    author: &str,
+    author: &'a str,
-    title: &str,
+    title: &'a str,
 }
 
+// Will the strings pointed to by book still be valid?
 fn main() {
     let book = Book {
         author: "George Orwell",

exercises/quizzes/quiz3.rs

@@ -12,18 +12,18 @@
 // block to support alphabetical report cards in addition to numerical ones.
 
 // TODO: Adjust the struct as described above.
-struct ReportCard {
+struct ReportCard<T> {
-    grade: f32,
+    grade: T,
     student_name: String,
     student_age: u8,
 }
 
 // TODO: Adjust the impl block as described above.
-impl ReportCard {
+impl<T: std::fmt::Display> ReportCard<T> {
     fn print(&self) -> String {
         format!(
             "{} ({}) - achieved a grade of {}",
-            &self.student_name, &self.student_age, &self.grade,
+            &self.student_name, &self.student_age, &self.grade
         )
     }
 }

solutions/16_lifetimes/lifetimes1.rs

@@ -1,4 +1,24 @@
-fn main() {
+// The Rust compiler needs to know how to check whether supplied references are
-    // DON'T EDIT THIS SOLUTION FILE!
+// valid, so that it can let the programmer know if a reference is at risk of
-    // It will be automatically filled after you finish the exercise.
+// going out of scope before it is used. Remember, references are borrows and do
+// not own their own data. What if their owner goes out of scope?
+
+fn longest<'a>(x: &'a str, y: &'a str) -> &'a str {
+    //    ^^^^     ^^          ^^          ^^
+    if x.len() > y.len() { x } else { y }
+}
+
+fn main() {
+    // You can optionally experiment here.
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_longest() {
+        assert_eq!(longest("abcd", "123"), "abcd");
+        assert_eq!(longest("abc", "1234"), "1234");
+    }
 }

solutions/16_lifetimes/lifetimes2.rs

@@ -1,4 +1,29 @@
-fn main() {
+fn longest<'a>(x: &'a str, y: &'a str) -> &'a str {
-    // DON'T EDIT THIS SOLUTION FILE!
+    if x.len() > y.len() { x } else { y }
-    // It will be automatically filled after you finish the exercise.
+}
+
+fn main() {
+    let string1 = String::from("long string is long");
+    // Solution1: You can move `strings2` out of the inner block so that it is
+    // not dropped before the print statement.
+    let string2 = String::from("xyz");
+    let result;
+    {
+        result = longest(&string1, &string2);
+    }
+    println!("The longest string is '{result}'");
+    // `string2` dropped at the end of the function.
+
+    // =========================================================================
+
+    let string1 = String::from("long string is long");
+    let result;
+    {
+        let string2 = String::from("xyz");
+        result = longest(&string1, &string2);
+        // Solution2: You can move the print statement into the inner block so
+        // that it is executed before `string2` is dropped.
+        println!("The longest string is '{result}'");
+        // `string2` dropped here (end of the inner scope).
+    }
 }

solutions/16_lifetimes/lifetimes3.rs

@@ -1,4 +1,18 @@
-fn main() {
+// Lifetimes are also needed when structs hold references.
-    // DON'T EDIT THIS SOLUTION FILE!
+
-    // It will be automatically filled after you finish the exercise.
+struct Book<'a> {
+    //     ^^^^ added a lifetime annotation
+    author: &'a str,
+    //       ^^
+    title: &'a str,
+    //      ^^
+}
+
+fn main() {
+    let book = Book {
+        author: "George Orwell",
+        title: "1984",
+    };
+
+    println!("{} by {}", book.title, book.author);
 }

solutions/quizzes/quiz3.rs

@@ -1,4 +1,65 @@
-fn main() {
+// An imaginary magical school has a new report card generation system written
-    // DON'T EDIT THIS SOLUTION FILE!
+// in Rust! Currently, the system only supports creating report cards where the
-    // It will be automatically filled after you finish the exercise.
+// 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.
+
+use std::fmt::Display;
+
+// Make the struct generic over `T`.
+struct ReportCard<T> {
+    //           ^^^
+    grade: T,
+    //     ^
+    student_name: String,
+    student_age: u8,
+}
+
+// To be able to print the grade, it has to implement the `Display` trait.
+impl<T: Display> ReportCard<T> {
+    //  ^^^^^^^ require that `T` implements `Display`.
+    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+",
+        );
+    }
 }