grade-school: Expect Option<Vec<String>> from grade; add stub file

exercises/grade-school/example.rs

@@ -21,7 +21,7 @@ impl School {
         s
     }
 
-    pub fn grade(&self, grade: u32) -> Option<&Vec<String>> {
-        self.grades.get(&grade)
+    pub fn grade(&self, grade: u32) -> Option<Vec<String>> {
+        self.grades.get(&grade).map(|v| v.iter().cloned().collect())
     }
 }

exercises/grade-school/src/lib.rs

@@ -0,0 +1,26 @@
+#[allow(unused_variables)]
+
+pub struct School {
+}
+
+impl School {
+    pub fn new() -> School {
+        unimplemented!()
+    }
+
+    pub fn add(&mut self, grade: u32, student: &str) {
+        unimplemented!()
+    }
+
+    pub fn grades(&self) -> Vec<u32> {
+        unimplemented!()
+    }
+
+    // If grade returned an `Option<&Vec<String>>`,
+    // the internal implementation would be forced to keep a `Vec<String>` to lend out.
+    // By returning an owned vector instead,
+    // the internal implementation is free to use whatever it chooses.
+    pub fn grade(&self, grade: u32) -> Option<Vec<String>> {
+        unimplemented!()
+    }
+}

exercises/grade-school/tests/grade-school.rs

@@ -1,7 +1,7 @@
 extern crate grade_school as school;
 
-fn stringvec_to_strvec(v: &Vec<String>) -> Vec<&str> {
-    v.iter().map(|s| s.as_ref()).collect()
+fn some_strings(v: Vec<&str>) -> Option<Vec<String>> {
+    Some(v.iter().map(|s| s.to_string()).collect())
 }
 
 #[test]
@@ -58,8 +58,8 @@ fn test_grade_when_no_students_have_that_grade() {
 fn test_grade_for_one_student() {
     let mut s = school::School::new();
     s.add(2, "Aimee");
-    assert_eq!(s.grade(2).map(|v| stringvec_to_strvec(v)),
-                Some(vec!["Aimee"]))
+    assert_eq!(s.grade(2),
+                some_strings(vec!["Aimee"]));
 }
 
 #[test]
@@ -69,8 +69,8 @@ fn test_grade_returns_students_sorted_by_name() {
     s.add(2, "James");
     s.add(2, "Blair");
     s.add(2, "Paul");
-    assert_eq!(s.grade(2).map(|v| stringvec_to_strvec(v)),
-               Some(vec!["Blair", "James", "Paul"]));
+    assert_eq!(s.grade(2),
+               some_strings(vec!["Blair", "James", "Paul"]));
 }
 
 #[test]
@@ -80,8 +80,8 @@ fn test_add_students_to_different_grades() {
     s.add(3, "Chelsea");
     s.add(7, "Logan");
     assert_eq!(s.grades(), vec!(3, 7));
-    assert_eq!(s.grade(3).map(|v| stringvec_to_strvec(v)),
-               Some(vec!["Chelsea"]));
-    assert_eq!(s.grade(7).map(|v| stringvec_to_strvec(v)),
-               Some(vec!["Logan"]));
+    assert_eq!(s.grade(3),
+               some_strings(vec!["Chelsea"]));
+    assert_eq!(s.grade(7),
+               some_strings(vec!["Logan"]));
 }