---

yaml
---
r: 35463
b: refs/heads/master
c: 65a1287
h: refs/heads/master
i:
  35461: c5f6dee
  35459: 385669b
  35455: fdecfd9
v: v3

Author: catamorphism

[refs]

@@ -1,5 +1,5 @@
 ---
-refs/heads/master: 01c0971172578ac170b3ae07c35ae416644ca1ef
+refs/heads/master: 65a1287f53c11718fa2cb153f2046af701c9cf9a
 refs/heads/snap-stage1: e33de59e47c5076a89eadeb38f4934f58a3618a6
 refs/heads/snap-stage3: eb8fd119c65c67f3b1b8268cc7341c22d39b7b61
 refs/heads/try: d324a424d8f84b1eb049b12cf34182bda91b0024

trunk/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