---

yaml
---
r: 39321
b: refs/heads/incoming
c: 65a1287
h: refs/heads/master
i:
  39319: eff7113
v: v3

Author: catamorphism

[refs]

@@ -6,7 +6,7 @@ refs/heads/try: 3d5418789064fdb463e872a4e651af1c628a3650
 refs/tags/release-0.1: 1f5c5126e96c79d22cb7862f75304136e204f105
 refs/heads/ndm: f3868061cd7988080c30d6d5bf352a5a5fe2460b
 refs/heads/try2: a810c03263670238bccd64cabb12a23a46e3a278
-refs/heads/incoming: 01c0971172578ac170b3ae07c35ae416644ca1ef
+refs/heads/incoming: 65a1287f53c11718fa2cb153f2046af701c9cf9a
 refs/heads/dist-snap: 22efa39382d41b084fde1719df7ae8ce5697d8c9
 refs/tags/release-0.2: c870d2dffb391e14efb05aa27898f1f6333a9596
 refs/tags/release-0.3: b5f0d0f648d9a6153664837026ba1be43d3e2503

branches/incoming/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