---

yaml
---
r: 34044
b: refs/heads/snap-stage3
c: 65a1287
h: refs/heads/master
v: v3

Author: catamorphism

[refs]

@@ -1,7 +1,7 @@
 ---
 refs/heads/master: cd6f24f9d14ac90d167386a56e7a6ac1f0318195
 refs/heads/snap-stage1: e33de59e47c5076a89eadeb38f4934f58a3618a6
-refs/heads/snap-stage3: 01c0971172578ac170b3ae07c35ae416644ca1ef
+refs/heads/snap-stage3: 65a1287f53c11718fa2cb153f2046af701c9cf9a
 refs/heads/try: d324a424d8f84b1eb049b12cf34182bda91b0024
 refs/tags/release-0.1: 1f5c5126e96c79d22cb7862f75304136e204f105
 refs/heads/ndm: f3868061cd7988080c30d6d5bf352a5a5fe2460b

branches/snap-stage3/doc/tutorial.md

@@ -1817,14 +1817,29 @@ struct Stack<T> {
     elements: ~[mut T]
 }
 
-enum Maybe<T> {
-    Just(T),
-    Nothing
+enum Option<T> {
+    Some(T),
+    None
 }
 ~~~~
 
 These declarations can be instantiated to valid types like `Set<int>`,
-`Stack<int>` and `Maybe<int>`.
+`Stack<int>` and `Option<int>`.
+
+The last type in that example, `Option`, appears frequently in Rust code.
+Because Rust does not have null pointers (except in unsafe code), we need
+another way to write a function whose result isn't defined on every possible
+combination of arguments of the appropriate types. The usual way is to write
+a function that returns `Option<T>` instead of `T`.
+
+~~~~
+fn radius(shape: Shape) -> Option<float> {
+   match shape {
+       Circle(_, radius) => Some(radius),
+       Rectangle(*)      => None
+   }      
+}
+~~~~
 
 The Rust compiler compiles generic functions very efficiently by
 *monomorphizing* them. *Monomorphization* is a fancy name for a simple