finish until lifetimes

solutions/16_lifetimes/lifetimes3.rs

@@ -1,4 +1,18 @@
-fn main() {
-    // DON'T EDIT THIS SOLUTION FILE!
-    // It will be automatically filled after you finish the exercise.
+// Lifetimes are also needed when structs hold references.
+
+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);
 }