auto merge of #13106 : CLUSTERfoo/rust/docs/labelled_breaks, r=brson

* Include tip given by Leo Testard in mailing list about labeled `break`
and `continue`:
https://mail.mozilla.org/pipermail/rust-dev/2014-March/009145.html
* cross-reference named lifetimes in tutorial -> lifetimes guide
* Broke named lifetimes section into two sub-sections.
* Added mention of `'static` lifetime.

Author: bors

src/doc/guide-lifetimes.md

@@ -559,9 +559,14 @@ points at a static constant).
 
 # Named lifetimes
 
-Let's look at named lifetimes in more detail. Named lifetimes allow
-for grouping of parameters by lifetime. For example, consider this
-function:
+Lifetimes can be named and referenced. For example, the special lifetime
+`'static`, which does not go out of scope, can be used to create global
+variables and communicate between tasks (see the manual for usecases).
+
+## Parameter Lifetimes
+
+Named lifetimes allow for grouping of parameters by lifetime.
+For example, consider this function:
 
 ~~~
 # struct Point {x: f64, y: f64}; // as before
@@ -655,6 +660,25 @@ fn select<'r, T>(shape: &Shape, threshold: f64,
 
 This is equivalent to the previous definition.
 
+## Labeled Control Structures
+
+Named lifetime notation can also be used to control the flow of execution:
+
+~~~
+'h: for i in range(0,10) {
+    'g: loop {
+        if i % 2 == 0 { continue 'h; }
+        if i == 9 { break 'h; }
+        break 'g;
+    }
+}
+~~~
+
+> ***Note:*** Labelled breaks are not currently supported within `while` loops.
+
+Named labels are hygienic and can be used safely within macros.
+See the macros guide section on hygiene for more details.
+
 # Conclusion
 
 So there you have it: a (relatively) brief tour of the lifetime

src/doc/guide-macros.md

@@ -398,6 +398,38 @@ position (in particular, not as an argument to yet another macro invocation),
 the expander will then proceed to evaluate `m2!()` (along with any other macro
 invocations `m1!(m2!())` produced).
 
+# Hygiene
+
+To prevent clashes, rust implements
+[hygienic macros](http://en.wikipedia.org/wiki/Hygienic_macro).
+
+As an example, `loop` and `for-loop` labels (discussed in the lifetimes guide)
+will not clash. The following code will print "Hello!" only once:
+
+~~~
+#[feature(macro_rules)];
+
+macro_rules! loop_x (
+    ($e: expr) => (
+        // $e will not interact with this 'x
+        'x: loop {
+            println!("Hello!");
+            $e
+        }
+    );
+)
+
+fn main() {
+    'x: loop {
+        loop_x!(break 'x);
+        println!("I am never printed.");
+    }
+}
+~~~
+
+The two `'x` names did not clash, which would have caused the loop
+to print "I am never printed" and to run forever.
+
 # A final note
 
 Macros, as currently implemented, are not for the faint of heart. Even

src/doc/tutorial.md

@@ -2103,7 +2103,8 @@ a `&T` pointer. `MutexArc` is an example of a *sharable* type with internal muta
 These are types that do not contain any data whose lifetime is bound to
 a particular stack frame. These are types that do not contain any
 references, or types where the only contained references
-have the `'static` lifetime.
+have the `'static` lifetime. (For more on named lifetimes and their uses, 
+see the [references and lifetimes guide][lifetimes].)
 
 > ***Note:*** These two traits were referred to as 'kinds' in earlier
 > iterations of the language, and often still are.