---

yaml
---
r: 54510
b: refs/heads/snap-stage3
c: 1e483c7
h: refs/heads/master
v: v3

Author: Diggory Hardy

[refs]

@@ -1,7 +1,7 @@
 ---
 refs/heads/master: 5f13e9ccc2e3328d4cd8ca49f84e6840dd998346
 refs/heads/snap-stage1: e33de59e47c5076a89eadeb38f4934f58a3618a6
-refs/heads/snap-stage3: 25b39b85da9544a4df9ce8201ac9878b1ec34ff5
+refs/heads/snap-stage3: 1e483c7b70a7369da3c1cd2c858cf2c3d455968c
 refs/heads/try: 8eb2bab100b42f0ba751552d8eff00eb2134c55a
 refs/tags/release-0.1: 1f5c5126e96c79d22cb7862f75304136e204f105
 refs/heads/ndm: f3868061cd7988080c30d6d5bf352a5a5fe2460b

branches/snap-stage3/doc/tutorial.md

@@ -1067,6 +1067,26 @@ let mut d = @mut 5; // mutable variable, mutable box
 d = @mut 15;
 ~~~~
 
+A mutable variable and an immutable variable can refer to the same box, given 
+that their types are compatible. Mutability of a box is a property of its type, 
+however, so for example a mutable handle to an immutable box cannot be 
+assigned a reference to a mutable box.
+
+~~~~
+let a = @1;     // immutable box
+let b = @mut 2; // mutable box
+
+let mut c : @int;       // declare a variable with type managed immutable int
+let mut d : @mut int;   // and one of type managed mutable int
+
+c = a;          // box type is the same, okay
+d = b;          // box type is the same, okay
+
+// but b cannot be assigned to c, or a to d
+c = b;          // error
+~~~~
+
+
 # Move semantics
 
 Rust uses a shallow copy for parameter passing, assignment and returning values
@@ -1081,6 +1101,16 @@ let y = x.clone(); // y is a newly allocated box
 let z = x; // no new memory allocated, x can no longer be used
 ~~~~
 
+Since in owned boxes mutabilility is a property of the owner, not the 
+box, mutable boxes may become immutable when they are moved, and vice-versa.
+
+~~~~
+let r = ~13;
+let mut s = r; // box becomes mutable
+*s += 1;
+let t = s; // box becomes immutable
+~~~~
+
 # Borrowed pointers
 
 Rust's borrowed pointers are a general purpose reference type. In contrast with
@@ -1191,7 +1221,7 @@ they are frozen:
 let x = @mut 5;
 let y = x;
 {
-    let y = &*y; // the managed box is now frozen
+    let z = &*y; // the managed box is now frozen
     // modifying it through x or y will cause a task failure
 }
 // the box is now unfrozen again

branches/snap-stage3/src/librust/rust.rc

@@ -64,7 +64,7 @@ static commands: &'static [Command<'static>] = &[
     Command{
         cmd: "run",
         action: Call(cmd_run),
-        usage_line: "build an executable, and run it",
+        usage_line: "build a executable, and run it",
         usage_full: UsgStr(
             "The run command is an shortcut for the command line \n\
              \"rustc <filename> -o <filestem>~ && ./<filestem>~\".\