---

yaml
---
r: 56702
b: refs/heads/try
c: 614d6da
h: refs/heads/master
v: v3

Author: bors

[refs]

@@ -2,7 +2,7 @@
 refs/heads/master: c081ffbd1e845687202a975ea2e698b623e5722f
 refs/heads/snap-stage1: e33de59e47c5076a89eadeb38f4934f58a3618a6
 refs/heads/snap-stage3: 79a2b2eafc3c766cecec8a5f76317693bae9ed17
-refs/heads/try: 08e2cf846aebf5a9f5e53881814976a3beee89a7
+refs/heads/try: 614d6da828969389871e01d1b8a17b3ccc1a5caa
 refs/tags/release-0.1: 1f5c5126e96c79d22cb7862f75304136e204f105
 refs/heads/ndm: f3868061cd7988080c30d6d5bf352a5a5fe2460b
 refs/heads/try2: 147ecfdd8221e4a4d4e090486829a06da1e0ca3c

branches/try/doc/tutorial.md

@@ -1067,6 +1067,28 @@ 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
+~~~~
+
+~~~~ {.xfail-test}
+// 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 +1103,16 @@ 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 mutability 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