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364 lines
10 KiB
Markdown
364 lines
10 KiB
Markdown
---
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name: Rust
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contributors:
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- ["P1start", "http://p1start.github.io/"]
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filename: learnrust.rs
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---
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Rust is a programming language developed by Mozilla Research.
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Rust combines low-level control over performance with high-level convenience and
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safety guarantees.
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It achieves these goals without requiring a garbage collector or runtime, making
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it possible to use Rust libraries as a "drop-in replacement" for C.
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Rust’s first release, 0.1, occurred in January 2012, and for 3 years development
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moved so quickly that until recently the use of stable releases was discouraged
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and instead the general advice was to use nightly builds.
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On May 15th 2015, Rust 1.0 was released with a complete guarantee of backward
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compatibility. Improvements to compile times and other aspects of the compiler are
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currently available in the nightly builds. Rust has adopted a train-based release
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model with regular releases every six weeks. Rust 1.1 beta was made available at
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the same time of the release of Rust 1.0.
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Although Rust is a relatively low-level language, it has some functional
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concepts that are generally found in higher-level languages. This makes
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Rust not only fast, but also easy and efficient to code in.
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```rust
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// This is a comment. Line comments look like this...
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// and extend multiple lines like this.
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/* Block comments
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/* can be nested. */ */
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/// Documentation comments look like this and support markdown notation.
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/// # Examples
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///
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/// ```
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/// let five = 5
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/// ```
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///////////////
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// 1. Basics //
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///////////////
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#[allow(dead_code)]
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// Functions
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// `i32` is the type for 32-bit signed integers
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fn add2(x: i32, y: i32) -> i32 {
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// Implicit return (no semicolon)
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x + y
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}
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#[allow(unused_variables)]
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#[allow(unused_assignments)]
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#[allow(dead_code)]
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// Main function
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fn main() {
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// Numbers //
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// Immutable bindings
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let x: i32 = 1;
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// Integer/float suffixes
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let y: i32 = 13i32;
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let f: f64 = 1.3f64;
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// Type inference
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// Most of the time, the Rust compiler can infer what type a variable is, so
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// you don’t have to write an explicit type annotation.
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// Throughout this tutorial, types are explicitly annotated in many places,
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// but only for demonstrative purposes. Type inference can handle this for
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// you most of the time.
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let implicit_x = 1;
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let implicit_f = 1.3;
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// Arithmetic
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let sum = x + y + 13;
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// Mutable variable
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let mut mutable = 1;
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mutable = 4;
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mutable += 2;
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// Strings //
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// String literals
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let x: &str = "hello world!";
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// Printing
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println!("{} {}", f, x); // 1.3 hello world
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// A `String` – a heap-allocated string
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// Stored as a `Vec<u8>` and always holds a valid UTF-8 sequence,
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// which is not null terminated.
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let s: String = "hello world".to_string();
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// A string slice – an immutable view into another string
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// This is basically an immutable pointer and length of a string – it
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// doesn’t actually contain the contents of a string, just a pointer to
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// the beginning and a length of a string buffer,
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// statically allocated or contained in another object (in this case, `s`).
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// The string slice is like a view `&[u8]` into `Vec<T>`.
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let s_slice: &str = &s;
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println!("{} {}", s, s_slice); // hello world hello world
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// Vectors/arrays //
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// A fixed-size array
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let four_ints: [i32; 4] = [1, 2, 3, 4];
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// A dynamic array (vector)
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let mut vector: Vec<i32> = vec![1, 2, 3, 4];
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vector.push(5);
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// A slice – an immutable view into a vector or array
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// This is much like a string slice, but for vectors
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let slice: &[i32] = &vector;
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// Use `{:?}` to print something debug-style
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println!("{:?} {:?}", vector, slice); // [1, 2, 3, 4, 5] [1, 2, 3, 4, 5]
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// Tuples //
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// A tuple is a fixed-size set of values of possibly different types
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let x: (i32, &str, f64) = (1, "hello", 3.4);
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// Destructuring `let`
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let (a, b, c) = x;
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println!("{} {} {}", a, b, c); // 1 hello 3.4
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// Indexing
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println!("{}", x.1); // hello
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//////////////
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// 2. Types //
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//////////////
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// Struct
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struct Point {
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x: i32,
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y: i32,
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}
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let origin: Point = Point { x: 0, y: 0 };
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// A struct with unnamed fields, called a ‘tuple struct’
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struct Point2(i32, i32);
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let origin2 = Point2(0, 0);
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// Basic C-like enum
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enum Direction {
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Left,
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Right,
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Up,
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Down,
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}
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let up = Direction::Up;
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// Enum with fields
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// If you want to make something optional, the standard
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// library has `Option`
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enum OptionalI32 {
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AnI32(i32),
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Nothing,
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}
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let two: OptionalI32 = OptionalI32::AnI32(2);
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let nothing = OptionalI32::Nothing;
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// Generics //
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struct Foo<T> { bar: T }
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// This is defined in the standard library as `Option`
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// `Option` is used in place of where a null pointer
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// would normally be used.
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enum Optional<T> {
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SomeVal(T),
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NoVal,
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}
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// Methods //
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impl<T> Foo<T> {
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// Methods take an explicit `self` parameter
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fn bar(&self) -> &T { // self is borrowed
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&self.bar
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}
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fn bar_mut(&mut self) -> &mut T { // self is mutably borrowed
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&mut self.bar
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}
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fn into_bar(self) -> T { // here self is consumed
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self.bar
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}
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}
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let a_foo = Foo { bar: 1 };
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println!("{}", a_foo.bar()); // 1
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// Traits (known as interfaces or typeclasses in other languages) //
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trait Frobnicate<T> {
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fn frobnicate(self) -> Option<T>;
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}
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impl<T> Frobnicate<T> for Foo<T> {
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fn frobnicate(self) -> Option<T> {
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Some(self.bar)
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}
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}
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let another_foo = Foo { bar: 1 };
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println!("{:?}", another_foo.frobnicate()); // Some(1)
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// Function pointer types //
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fn fibonacci(n: u32) -> u32 {
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match n {
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0 => 1,
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1 => 1,
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_ => fibonacci(n - 1) + fibonacci(n - 2),
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}
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}
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type FunctionPointer = fn(u32) -> u32;
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let fib : FunctionPointer = fibonacci;
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println!("Fib: {}", fib(4)); // 5
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/////////////////////////
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// 3. Pattern matching //
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/////////////////////////
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let foo = OptionalI32::AnI32(1);
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match foo {
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OptionalI32::AnI32(n) => println!("it’s an i32: {}", n),
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OptionalI32::Nothing => println!("it’s nothing!"),
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}
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// Advanced pattern matching
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struct FooBar { x: i32, y: OptionalI32 }
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let bar = FooBar { x: 15, y: OptionalI32::AnI32(32) };
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match bar {
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FooBar { x: 0, y: OptionalI32::AnI32(0) } =>
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println!("The numbers are zero!"),
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FooBar { x: n, y: OptionalI32::AnI32(m) } if n == m =>
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println!("The numbers are the same"),
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FooBar { x: n, y: OptionalI32::AnI32(m) } =>
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println!("Different numbers: {} {}", n, m),
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FooBar { x: _, y: OptionalI32::Nothing } =>
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println!("The second number is Nothing!"),
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}
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/////////////////////
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// 4. Control flow //
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/////////////////////
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// `for` loops/iteration
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let array = [1, 2, 3];
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for i in array {
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println!("{}", i);
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}
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// Ranges
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for i in 0u32..10 {
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print!("{} ", i);
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}
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println!("");
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// prints `0 1 2 3 4 5 6 7 8 9 `
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// `if`
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if 1 == 1 {
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println!("Maths is working!");
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} else {
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println!("Oh no...");
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}
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// `if` as expression
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let value = if true {
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"good"
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} else {
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"bad"
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};
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// `while` loop
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while 1 == 1 {
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println!("The universe is operating normally.");
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// break statement gets out of the while loop.
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// It avoids useless iterations.
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break
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}
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// Infinite loop
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loop {
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println!("Hello!");
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// break statement gets out of the loop
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break
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}
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/////////////////////////////////
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// 5. Memory safety & pointers //
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/////////////////////////////////
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// Owned pointer – only one thing can ‘own’ this pointer at a time
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// This means that when the `Box` leaves its scope, it will be automatically deallocated safely.
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let mut mine: Box<i32> = Box::new(3);
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*mine = 5; // dereference
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// Here, `now_its_mine` takes ownership of `mine`. In other words, `mine` is moved.
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let mut now_its_mine = mine;
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*now_its_mine += 2;
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println!("{}", now_its_mine); // 7
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// println!("{}", mine); // this would not compile because `now_its_mine` now owns the pointer
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// Reference – an immutable pointer that refers to other data
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// When a reference is taken to a value, we say that the value has been ‘borrowed’.
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// While a value is borrowed immutably, it cannot be mutated or moved.
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// A borrow is active until the last use of the borrowing variable.
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let mut var = 4;
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var = 3;
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let ref_var: &i32 = &var;
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println!("{}", var); // Unlike `mine`, `var` can still be used
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println!("{}", *ref_var);
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// var = 5; // this would not compile because `var` is borrowed
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// *ref_var = 6; // this would not either, because `ref_var` is an immutable reference
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ref_var; // no-op, but counts as a use and keeps the borrow active
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var = 2; // ref_var is no longer used after the line above, so the borrow has ended
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// Mutable reference
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// While a value is mutably borrowed, it cannot be accessed at all.
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let mut var2 = 4;
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let ref_var2: &mut i32 = &mut var2;
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*ref_var2 += 2; // '*' is used to point to the mutably borrowed var2
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println!("{}", *ref_var2); // 6 , // var2 would not compile.
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// ref_var2 is of type &mut i32, so stores a reference to an i32, not the value.
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// var2 = 2; // this would not compile because `var2` is borrowed.
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ref_var2; // no-op, but counts as a use and keeps the borrow active until here
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}
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```
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## Further reading
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For a deeper-yet-still-fast explanation into Rust and its symbols/keywords, the
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[half-hour to learn Rust](https://fasterthanli.me/articles/a-half-hour-to-learn-rust)
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article by Fasterthanlime explains (almost) everything in a clear and concise way!
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There’s a lot more to Rust—this is just the basics of Rust so you can understand
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the most important things. To learn more about Rust, read [The Rust Programming
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Language](http://doc.rust-lang.org/book/index.html) and check out the
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[/r/rust](http://reddit.com/r/rust) subreddit. The folks on the #rust channel on
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irc.mozilla.org are also always keen to help newcomers.
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You can also try out features of Rust with an online compiler at the official
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[Rust Playground](https://play.rust-lang.org) or on the main
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[Rust website](http://rust-lang.org).
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