[rust/en] Update the Rust tutorial

This adjusts the English Rust tutorial for changes to the language and
generally tweaks a few other things.

Fixes #860.

rust.html.markdown

@@ -7,9 +7,13 @@ filename: learnrust.rs
 
 Rust is an in-development programming language developed by Mozilla Research.
 It is relatively unique among systems languages in that it can assert memory
-safety *at compile time*. Rust’s first alpha release occurred in January
+safety *at compile time* without resorting to garbage collection. Rust’s first
-2012, and development moves so quickly that at the moment the use of stable
+release, 0.1, occurred in January 2012, and development moves so quickly that at
-releases is discouraged, and instead one should use nightly builds.
+the moment the use of stable releases is discouraged, and instead one should use
+nightly builds. On January 9 2015, Rust 1.0 Alpha was released, and the rate of
+changes to the Rust compiler that break existing code has dropped significantly
+since. However, a complete guarantee of backward compatibility will not exist
+until the final 1.0 release.
 
 Although Rust is a relatively low-level language, Rust has some functional
 concepts that are generally found in higher-level languages. This makes
@@ -24,7 +28,8 @@ Rust not only fast, but also easy and efficient to code in.
 ///////////////
 
 // Functions
-fn add2(x: int, y: int) -> int {
+// `i32` is the type for 32-bit signed integers
+fn add2(x: i32, y: i32) -> i32 {
     // Implicit return (no semicolon)
     x + y
 }
@@ -34,71 +39,90 @@ fn main() {
     // Numbers //
 
     // Immutable bindings
-    let x: int = 1;
+    let x: i32 = 1;
 
     // Integer/float suffixes
-    let y: int = 13i;
+    let y: i32 = 13i32;
     let f: f64 = 1.3f64;
 
     // Type inference
-    let implicit_x = 1i;
+    // Most of the time, the Rust compiler can infer what type a variable is, so
-    let implicit_f = 1.3f64;
+    // you don’t have to write an explicit type annotation.
+    // Throughout this tutorial, types are explicitly annotated in many places,
+    // but only for demonstrative purposes. Type inference can handle this for
+    // you most of the time.
+    let implicit_x = 1;
+    let implicit_f = 1.3;
 
-    // Maths
+    // Arithmetic
-    let sum = x + y + 13i;
+    let sum = x + y + 13;
 
     // Mutable variable
     let mut mutable = 1;
+    mutable = 4;
     mutable += 2;
 
     // Strings //
-    
+
     // String literals
-    let x: &'static str = "hello world!";
+    let x: &str = "hello world!";
 
     // Printing
     println!("{} {}", f, x); // 1.3 hello world
 
-    // A `String` - a heap-allocated string
+    // A `String` – a heap-allocated string
     let s: String = "hello world".to_string();
 
-    // A string slice - an immutable view into another string
+    // A string slice – an immutable view into another string
-    // This is basically an immutable pointer to a string - it doesn’t
+    // This is basically an immutable pointer to a string – it doesn’t
-    // actually contain the characters of a string, just a pointer to
+    // actually contain the contents of a string, just a pointer to
     // something that does (in this case, `s`)
-    let s_slice: &str = s.as_slice();
+    let s_slice: &str = &*s;
 
     println!("{} {}", s, s_slice); // hello world hello world
 
     // Vectors/arrays //
 
     // A fixed-size array
-    let four_ints: [int, ..4] = [1, 2, 3, 4];
+    let four_ints: [i32; 4] = [1, 2, 3, 4];
 
-    // A dynamically-sized vector
+    // A dynamic array (vector)
-    let mut vector: Vec<int> = vec![1, 2, 3, 4];
+    let mut vector: Vec<i32> = vec![1, 2, 3, 4];
     vector.push(5);
 
-    // A slice - an immutable view into a vector or array
+    // A slice – an immutable view into a vector or array
     // This is much like a string slice, but for vectors
-    let slice: &[int] = vector.as_slice();
+    let slice: &[i32] = &*vector;
 
-    println!("{} {}", vector, slice); // [1, 2, 3, 4, 5] [1, 2, 3, 4, 5]
+    // Use `{:?}` to print something debug-style
+    println!("{:?} {:?}", vector, slice); // [1, 2, 3, 4, 5] [1, 2, 3, 4, 5]
+
+    // Tuples //
+
+    // A tuple is a fixed-size set of values of possibly different types
+    let x: (i32, &str, f64) = (1, "hello", 3.4);
+
+    // Destructuring `let`
+    let (a, b, c) = x;
+    println!("{} {} {}", a, b, c); // 1 hello 3.4
+
+    // Indexing
+    println!("{}", x.1); // hello
 
     //////////////
     // 2. Types //
     //////////////
-    
+
     // Struct
     struct Point {
-        x: int,
+        x: i32,
-        y: int,
+        y: i32,
     }
 
     let origin: Point = Point { x: 0, y: 0 };
 
-    // Tuple struct
+    // A struct with unnamed fields, called a ‘tuple struct’
-    struct Point2(int, int);
+    struct Point2(i32, i32);
 
     let origin2 = Point2(0, 0);
 
@@ -110,16 +134,16 @@ fn main() {
         Down,
     }
 
-    let up = Up;
+    let up = Direction::Up;
 
     // Enum with fields
-    enum OptionalInt {
+    enum OptionalI32 {
-        AnInt(int),
+        AnI32(i32),
         Nothing,
     }
 
-    let two:     OptionalInt = AnInt(2);
+    let two: OptionalI32 = OptionalI32::AnI32(2);
-    let nothing: OptionalInt = Nothing;
+    let nothing = OptionalI32::Nothing;
 
     // Generics //
 
@@ -140,10 +164,10 @@ fn main() {
         }
     }
 
-    let a_foo = Foo { bar: 1i };
+    let a_foo = Foo { bar: 1 };
     println!("{}", a_foo.get_bar()); // 1
 
-    // Traits (interfaces) //
+    // Traits (known as interfaces or typeclasses in other languages) //
 
     trait Frobnicate<T> {
         fn frobnicate(self) -> Option<T>;
@@ -155,30 +179,31 @@ fn main() {
         }
     }
 
-    println!("{}", a_foo.frobnicate()); // Some(1)
+    let another_foo = Foo { bar: 1 };
+    println!("{:?}", another_foo.frobnicate()); // Some(1)
 
     /////////////////////////
     // 3. Pattern matching //
     /////////////////////////
-    
+
-    let foo = AnInt(1);
+    let foo = OptionalI32::AnI32(1);
     match foo {
-        AnInt(n) => println!("it’s an int: {}", n),
+        OptionalI32::AnI32(n) => println!("it’s an i32: {}", n),
-        Nothing  => println!("it’s nothing!"),
+        OptionalI32::Nothing  => println!("it’s nothing!"),
     }
 
     // Advanced pattern matching
-    struct FooBar { x: int, y: OptionalInt }
+    struct FooBar { x: i32, y: OptionalI32 }
-    let bar = FooBar { x: 15, y: AnInt(32) };
+    let bar = FooBar { x: 15, y: OptionalI32::AnI32(32) };
 
     match bar {
-        FooBar { x: 0, y: AnInt(0) } =>
+        FooBar { x: 0, y: OptionalI32::AnI32(0) } =>
             println!("The numbers are zero!"),
-        FooBar { x: n, y: AnInt(m) } if n == m =>
+        FooBar { x: n, y: OptionalI32::AnI32(m) } if n == m =>
             println!("The numbers are the same"),
-        FooBar { x: n, y: AnInt(m) } =>
+        FooBar { x: n, y: OptionalI32::AnI32(m) } =>
             println!("Different numbers: {} {}", n, m),
-        FooBar { x: _, y: Nothing } =>
+        FooBar { x: _, y: OptionalI32::Nothing } =>
             println!("The second number is Nothing!"),
     }
 
@@ -187,19 +212,20 @@ fn main() {
     /////////////////////
 
     // `for` loops/iteration
-    let array = [1i, 2, 3];
+    let array = [1, 2, 3];
     for i in array.iter() {
         println!("{}", i);
     }
 
-    for i in range(0u, 10) {
+    // Ranges
+    for i in 0u32..10 {
         print!("{} ", i);
     }
     println!("");
     // prints `0 1 2 3 4 5 6 7 8 9 `
 
     // `if`
-    if 1i == 1 {
+    if 1 == 1 {
         println!("Maths is working!");
     } else {
         println!("Oh no...");
@@ -213,7 +239,7 @@ fn main() {
     };
 
     // `while` loop
-    while 1i == 1 {
+    while 1 == 1 {
         println!("The universe is operating normally.");
     }
 
@@ -225,40 +251,49 @@ fn main() {
     /////////////////////////////////
     // 5. Memory safety & pointers //
     /////////////////////////////////
-    
+
-    // Owned pointer - only one thing can ‘own’ this pointer at a time
+    // Owned pointer – only one thing can ‘own’ this pointer at a time
-    let mut mine: Box<int> = box 3;
+    // This means that when the `Box` leaves its scope, it can be automatically deallocated safely.
+    let mut mine: Box<i32> = Box::new(3);
     *mine = 5; // dereference
+    // Here, `now_its_mine` takes ownership of `mine`. In other words, `mine` is moved.
     let mut now_its_mine = mine;
     *now_its_mine += 2;
-    println!("{}", now_its_mine); // 7
-    // println!("{}", mine); // this would error
 
-    // Reference - an immutable pointer that refers to other data
+    println!("{}", now_its_mine); // 7
-    let mut var = 4i;
+    // println!("{}", mine); // this would not compile because `now_its_mine` now owns the pointer
+
+    // Reference – an immutable pointer that refers to other data
+    // When a reference is taken to a value, we say that the value has been ‘borrowed’.
+    // While a value is borrowed immutably, it cannot be mutated or moved.
+    // A borrow lasts until the end of the scope it was created in.
+    let mut var = 4;
     var = 3;
-    let ref_var: &int = &var;
+    let ref_var: &i32 = &var;
+
     println!("{}", var); // Unlike `box`, `var` can still be used
     println!("{}", *ref_var);
-    // var = 5; // this would error
+    // var = 5; // this would not compile because `var` is borrowed
-    // *ref_var = 6; // this would too
+    // *ref_var = 6; // this would too, because `ref_var` is an immutable reference
 
     // Mutable reference
-    let mut var2 = 4i;
+    // While a value is mutably borrowed, it cannot be accessed at all.
-    let ref_var2: &mut int = &mut var2;
+    let mut var2 = 4;
+    let ref_var2: &mut i32 = &mut var2;
     *ref_var2 += 2;
+
     println!("{}", *ref_var2); // 6
-    // var2 = 2; // this would error
+    // var2 = 2; // this would not compile because `var2` is borrowed
 }
 ```
 
 ## Further reading
 
-There’s a lot more to Rust—this is just the basics of Rust so you can
+There’s a lot more to Rust—this is just the basics of Rust so you can understand
-understand the most important things. To learn more about Rust, read [The Rust
+the most important things. To learn more about Rust, read [The Rust Programming
-Guide](http://doc.rust-lang.org/guide.html) and check out the
+Language](http://doc.rust-lang.org/book/index.html) and check out the
-[/r/rust](http://reddit.com/r/rust) subreddit. The folks on the #rust channel
+[/r/rust](http://reddit.com/r/rust) subreddit. The folks on the #rust channel on
-on irc.mozilla.org are also always keen to help newcomers.
+irc.mozilla.org are also always keen to help newcomers.
 
 You can also try out features of Rust with an online compiler at the official
 [Rust playpen](http://play.rust-lang.org) or on the main