Merge pull request #437 from cbzehner/nth-prime

nth-prime: Provide a function template

Author: coriolinus

exercises/nth-prime/example.rs

@@ -9,10 +9,10 @@ fn is_prime(n: u32) -> bool {
    return true;
 }
 
-pub fn nth(n: u32) -> Result<u32, ()> {
+pub fn nth(n: u32) -> Option<u32> {
     match n {
-        0 => Err(()),
-        1 => Ok(2),
+        0 => None,
+        1 => Some(2),
         _ => {
             let mut count: u32 = 1;
             let mut candidate: u32 = 1;
@@ -22,7 +22,7 @@ pub fn nth(n: u32) -> Result<u32, ()> {
                     count += 1;
                 }
             }
-            Ok(candidate)
+            Some(candidate)
         }
     }
 }

exercises/nth-prime/src/lib.rs

@@ -0,0 +1,3 @@
+pub fn nth(n: u32) -> Option<u32> {
+    unimplemented!("What is the {}th prime number?", n)
+}

exercises/nth-prime/tests/nth-prime.rs

@@ -2,29 +2,29 @@ extern crate nth_prime as np;
 
 #[test]
 fn test_first_prime() {
-    assert_eq!(np::nth(1), Ok(2));
+    assert_eq!(np::nth(1), Some(2));
 }
 
 #[test]
 #[ignore]
 fn test_second_prime() {
-    assert_eq!(np::nth(2), Ok(3));
+    assert_eq!(np::nth(2), Some(3));
 }
 
 #[test]
 #[ignore]
 fn test_sixth_prime() {
-    assert_eq!(np::nth(6), Ok(13));
+    assert_eq!(np::nth(6), Some(13));
 }
 
 #[test]
 #[ignore]
 fn test_big_prime() {
-    assert_eq!(np::nth(10001), Ok(104743));
+    assert_eq!(np::nth(10001), Some(104743));
 }
 
 #[test]
 #[ignore]
 fn test_zeroth_prime() {
-    assert!(np::nth(0).is_err());
+    assert_eq!(np::nth(0), None);
 }