// This is a comment. Line comments look like this...
// and extend multiple lines like this.
/// Documentation comments look like this and support markdown notation.
/// # Examples
///
/// ```
/// let five = 5
/// ```
///////////////
// 1. Basics //
///////////////
#[allow(dead_code)]
// Functions
// `i32` is the type for 32-bit signed integers
fn add2(x: i32, y: i32) -> i32 {
// Implicit return (no semicolon)
x + y
}
#[allow(unused_variables)]
#[allow(unused_assignments)]
#[allow(dead_code)]
// Main function
fn main() {
// Numbers //
// Immutable bindings
let x: i32 = 1;
// Integer/float suffixes
let y: i32 = 13i32;
let f: f64 = 1.3f64;
// Type inference
// Most of the time, the Rust compiler can infer what type a variable is, so
// 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;
// Arithmetic
let sum = x + y + 13;
// Mutable variable
let mut mutable = 1;
mutable = 4;
mutable += 2;
// Strings //
// String literals
let x: &str = "hello world!";
// Printing
println!("{} {}", f, x); // 1.3 hello world
// A `String` – a heap-allocated string
// Stored as a `Vec<u8>` and always hold a valid UTF-8 sequence,
// which is not null terminated.
let s: String = "hello world".to_string();
// A string slice – an immutable view into another string
// This is basically an immutable pair of pointers to a string – it doesn’t
// actually contain the contents of a string, just a pointer to
// the begin and a pointer to the end of a string buffer,
// statically allocated or contained in another object (in this case, `s`).
// The string slice is like a view `&[u8]` into `Vec<T>`.
let s_slice: &str = &s;
println!("{} {}", s, s_slice); // hello world hello world
// Vectors/arrays //
// A fixed-size array
let four_ints: [i32; 4] = [1, 2, 3, 4];
// A dynamic array (vector)
let mut vector: Vec<i32> = vec![1, 2, 3, 4];
vector.push(5);
// A slice – an immutable view into a vector or array
// This is much like a string slice, but for vectors
let slice: &[i32] = &vector;
// 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: i32,
y: i32,
}
let origin: Point = Point { x: 0, y: 0 };
// A struct with unnamed fields, called a ‘tuple struct’
struct Point2(i32, i32);
let origin2 = Point2(0, 0);
// Basic C-like enum
enum Direction {
Left,
Right,
Up,
Down,
}
let up = Direction::Up;
// Enum with fields
enum OptionalI32 {
AnI32(i32),
Nothing,
}
let two: OptionalI32 = OptionalI32::AnI32(2);
let nothing = OptionalI32::Nothing;
// Generics //
struct Foo<T> { bar: T }
// This is defined in the standard library as `Option`
enum Optional<T> {
SomeVal(T),
NoVal,
}
// Methods //
impl<T> Foo<T> {
// Methods take an explicit `self` parameter
fn bar(&self) -> &T { // self is borrowed
&self.bar
}
fn bar_mut(&mut self) -> &mut T { // self is mutably borrowed
&mut self.bar
}
fn into_bar(self) -> T { // here self is consumed
self.bar
}
}
let a_foo = Foo { bar: 1 };
println!("{}", a_foo.bar()); // 1
// Traits (known as interfaces or typeclasses in other languages) //
trait Frobnicate<T> {
fn frobnicate(self) -> Option<T>;
}
impl<T> Frobnicate<T> for Foo<T> {
fn frobnicate(self) -> Option<T> {
Some(self.bar)
}
}
let another_foo = Foo { bar: 1 };
println!("{:?}", another_foo.frobnicate()); // Some(1)
// Function pointer types //
fn fibonacci(n: u32) -> u32 {
match n {
0 => 1,
1 => 1,
_ => fibonacci(n - 1) + fibonacci(n - 2),
}
}
type FunctionPointer = fn(u32) -> u32;
let fib : FunctionPointer = fibonacci;
println!("Fib: {}", fib(4)); // 5
/////////////////////////
// 3. Pattern matching //
/////////////////////////
let foo = OptionalI32::AnI32(1);
match foo {
OptionalI32::AnI32(n) => println!("it’s an i32: {}", n),
OptionalI32::Nothing => println!("it’s nothing!"),
}
// Advanced pattern matching
struct FooBar { x: i32, y: OptionalI32 }
let bar = FooBar { x: 15, y: OptionalI32::AnI32(32) };
match bar {
FooBar { x: 0, y: OptionalI32::AnI32(0) } =>
println!("The numbers are zero!"),
FooBar { x: n, y: OptionalI32::AnI32(m) } if n == m =>
println!("The numbers are the same"),
FooBar { x: n, y: OptionalI32::AnI32(m) } =>
println!("Different numbers: {} {}", n, m),
FooBar { x: _, y: OptionalI32::Nothing } =>
println!("The second number is Nothing!"),
}
/////////////////////
// 4. Control flow //
/////////////////////
// `for` loops/iteration
let array = [1, 2, 3];
for i in array {
println!("{}", i);
}
// Ranges
for i in 0u32..10 {
print!("{} ", i);
}
println!("");
// prints `0 1 2 3 4 5 6 7 8 9 `
// `if`
if 1 == 1 {
println!("Maths is working!");
} else {
println!("Oh no...");
}
// `if` as expression
let value = if true {
"good"
} else {
"bad"
};
// `while` loop
while 1 == 1 {
println!("The universe is operating normally.");
// break statement gets out of the while loop.
// It avoids useless iterations.
break
}
// Infinite loop
loop {
println!("Hello!");
// break statement gets out of the loop
break
}
/////////////////////////////////
// 5. Memory safety & pointers //
/////////////////////////////////
// Owned pointer – only one thing can ‘own’ this pointer at a time
// 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 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 is active until the last use of the borrowing variable.
let mut var = 4;
var = 3;
let ref_var: &i32 = &var;
println!("{}", var); // Unlike `mine`, `var` can still be used
println!("{}", *ref_var);
// var = 5; // this would not compile because `var` is borrowed
// *ref_var = 6; // this would not either, because `ref_var` is an immutable reference
ref_var; // no-op, but counts as a use and keeps the borrow active
var = 2; // ref_var is no longer used after the line above, so the borrow has ended
// Mutable reference
// While a value is mutably borrowed, it cannot be accessed at all.
let mut var2 = 4;
let ref_var2: &mut i32 = &mut var2;
*ref_var2 += 2; // '*' is used to point to the mutably borrowed var2
println!("{}", *ref_var2); // 6 , // var2 would not compile.
// ref_var2 is of type &mut i32, so stores a reference to an i32, not the value.
// var2 = 2; // this would not compile because `var2` is borrowed.
ref_var2; // no-op, but counts as a use and keeps the borrow active until here
}
$
cheat.sh
learnxinyminutes-docs