Getting started!

Rustup, Cargo & Hello World

Rustup

Installer for the Rust toolchain

 

Let’s install Rust!

https://rustup.rs

 

Afterwards:

The cargo command should be runnable in your shell

$ cargo new hello_world
     Created binary (application) `hello_world` package
$ cd testing
$ cargo run
   Compiling hello_world v0.1.0 (/tmp/testing)
    Finished dev [unoptimized + debuginfo] target(s) in 0.83s
     Running `target/debug/hello_world`
Hello, world!

Creating and running our first program

fn main() {
    println!("Hello, world!");
}

src/main.rs

The Rust docs are very useful:

https://doc.rust-lang.org/std/index.html

fn main() {
    for n in 0..10 {
        let n_is_even = is_even(n);
        if n_is_even {
            println!("{} is even", n);
        } else {
            println!("{} is odd", n);
        }
    }
}

fn is_even(num: i32) -> bool {
    num % 2 == 0
}

src/main.rs

0 is even
1 is odd
2 is even
3 is odd
4 is even
5 is odd
6 is even
7 is odd
8 is even
9 is odd
fn main() {
    for n in 0..10 {
        let n_is_even = is_even(n);
        if n_is_even {
            println!("{} is even", n);
        } else {
            println!("{} is odd", n);
        }
    }
}

fn is_even(num: i32) -> bool {
    num & 1 == 0
}

src/main.rs

Let's do a FizzBuzz

fn main() {
    for n in 0..10 {
        let n_is_even = is_even(n);
        if n_is_even {
            println!("{} is even", n);
        // } else if <condition> {
        } else {
            println!("{} is odd", n);
        }
    }
}

fn is_even(num: i32) -> bool {
    num % 2 == 0
}

If multiple of 3, print Fizz

If multiple of 5, print Buzz

If multiple of both print, FizzBuzz instead

Else, print the number

fn main() {
    for n in 0..10 {
        let is_mul_3 = n % 3 == 0;
        let is_mul_5 = n % 5 == 0;
    
        if is_mul_3 && is_mul_5 {
            println!("FizzBuzz");
        } else if is_mul_3 {
            println!("Fizz");
        } else if is_mul_5 {
            println!("Buzz");
        } else {
            println!("{}", n);
        }
    }
}

fn main() {
    for n in 0..10 {
        match (n % 3, n % 5) {
            (0, 0) => println!("FizzBuzz"),
            (0, _) => println!("Fizz"),
            (_, 0) => println!("Buzz"),
            (_, _) => println!("{}", n),
        }
    }
}

fn main() {
    for n in 0..10 {
        let is_mul_3 = n % 3 == 0;
        let is_mul_5 = n % 5 == 0;
        if is_mul_3 && is_mul_5 {
            println!("FizzBuzz");
        } else if is_mul_3 {
            println!("Fizz");
        } else if is_mul_5 {
            println!("Buzz");
        } else {
            println!("{}", n);
        }
    }
}

Intro Tour

  • struct/class
  • Methods
  • enum
  • unions
  • copy
  • Interfaces
  • Inheritance
  • Polymorphism
  • Templates
  • struct
  • Associated Functions
  • enum
  • enum with fields
  • move
  • traits (ish)
  • Nope! (traits ish)
  • Polymorphism
  • Generics

my_library_crate

  • root module
    • api
    • data
    • utils

my_binary_crate

  • root module
    • ui

Traits

→

→

Sortable

Hashable

implements Ord trait

implements Hash trait

Time

string

&string

let num_1 = 213;

let num_2: u8 = num_1;

Type Inference

TODO Concept Prototypes

  • crates
  • traits
  • borrows/references/lifetimes

Ownership and Borrowing

Traits

Typing

FP Concepts

Safe Multithreading

Unsafe Blocks

Cargo

Basic Types

i8    / u8
i16   / u16
i32   / u32
i64   / u64
i128  / u128

isize / usize

f32

f64

Numeric primitive types

Explicitly sized

Pointer-sized

Floating point

let num = 13i32;
let num: i32 = 13;
let large_num = 32i64;

let smaller_num = large_num as i16;

assert_eq!(smaller_num, 32);

Other primitive types

bool

Boolean

()

Unit type

char

Unicode scalar

Composite Data Structures

Struct

/// Struct which represents a book in our
/// program.
struct Book {
    name: String,
    /// The ISBN number of the book, which 
    /// should be unique for each book.
    isbn: u64,
}

Struct

/// Struct which represents a book in our
/// program.
struct Book {
    name: String,
    /// The ISBN number of the book, which 
    /// should be unique for each book.
    isbn: u64,
}

struct Version(u32, u32, u32);

struct Service;

Struct

struct Book {
    name: String,
    isbn: u64,
}

struct Version(u32, u32, u32);

fn main() {
    let book = Book {
        name: String::from("Cryptonomicon")
        isbn: 0380973464,
    };
    
    let version = Version(1, 8, 2)
}
struct Counter {
    count: u32,
}

impl Counter {
    
    fn new() -> Self {
        Counter {
            count: 0,
        }
    }
    
    fn increment(&mut self, inc: u32) {
        self.count += inc;
    }
    
}

fn main() {
    let mut counter = Counter::new();
    counter.increment(5);
}
struct Counter {
    count: u32,
}

impl Counter {

    const MAX: u32 = u32::MAX;

}

Tuple

let a: (u32, u8) = (1, 1);
struct A(u32, u32);
struct B(u32, u32);

fn my_func(a: A) {}

fn main() {
    let val = B(12, 13);
    my_func(val);
}
fn my_func(a: (u32, u32)) {}

fn main() {
    let val = (12, 13);
    my_func(val);
}
error[E0308]: mismatched types
 --> src/main.rs:8:13
  |
8 |     my_func(val);
  |             ^^^ expected struct `A`, found struct `B`
()
(u32,)
(u32, u32)
(u32, u32, u32)
(u32, u32, u32, u32)
[...]

()

struct A;

struct A();

struct A(u32, u32);

(u32, u32)

by Structure

by Identity

Enum

enum BookKind {
    Fantasy,
    SciFi,
    Action,
    Mystery,
}
enum Publisher {
    SelfPublished,
    Company {
        name: String,
        org_no: u64,
    },
}
enum Publisher {
    SelfPublished,
    Company {
        name: String,
        org_no: u64,
    },
}

fn main() {
    let variant_a = Publisher::SelfPublished;
    
    let variant_b = Publisher::Company {
        name: "Avon".into(),
        org_no: 1128763212,
    };
}
fn main() {
    let publisher = [...];
    
    match publisher {
    	Publisher::SelfPublished => 
            println!("The book was self published"),
        Publisher::Company { name, org_no } =>
            println!(
                "The book was published by {} ({})", 
                name, org_no
            ),
    }
}

std::optional

The class template std::optional manages an optional contained value, i.e. a value that may or may not be present.

A common use case for optional is the return value of a function that may fail.

Given we had a way to do type parameters, could something like this be represented well with an enum?

enum

struct MyStruct<A, B> {
    var_a: A,
    var_b: A,
    var_c: B,
}

Derives

#[derive(Copy, Clone)]
struct Counter {
    num: u32,
    step: u32,
}

Derives

#[derive(Debug)]
struct Counter {
    num: u32,
    step: u32,
}
let counter = Counter {
    num: 31,
    step: 1,
};

println!("my struct: {:?}");
my struct: Counter { num: 31, step: 1 }
  • Ord/PartialOrd
  • Eq/PartialEq
  • Hash
  • Default
  • Serialize/Deserialize

Unions

Honorary Mention:

Control Flow

let num = 5;

if num > 10 {
    println!("yay!");
} else {
    println!("nay!");
}

let num = 5;

if num {
    println!("yay!");
} else {
    println!("nay!");
}

error[E0308]: mismatched types
 --> src/main.rs:4:8
  |
4 |     if num {
  |        ^^^ expected `bool`, found integer

cargo run

let num = 5;

let string = if num > 10 {
    "yay"
} else {
    "nay"
};

println!("{}", string);

let num = 5;

match num {
    4 => println!("four"),
    5 => println!("five"),
    _ => println!("other"),
}
let num = 5;

match num {
    4 => println!("four"),
    5 => println!("five"),
}
error[E0004]: non-exhaustive patterns: `i32::MIN..=3_i32` and 
              `6_i32..=i32::MAX` not covered
 --> src/main.rs:5:7
  |
5 | match num {
  |       ^^^ patterns `i32::MIN..=3_i32` and `6_i32..=i32::MAX` 
              not covered
  |
  = help: ensure that all possible cases are being handled, 
          possibly by adding wildcards or more match arms
  = note: the matched value is of type `i32`

cargo run

struct MyData {
    cond: bool,
    num: i32,
}

enum MyEnum {
    A {
        data: MyData,
    },
    B {
        num: i32,
    },
}

fn main() {
    let item = MyEnum::A { 
        data: MyData { cond: false },
    };

    match item {
        MyEnum::A { data: MyData { cond: true, .. }} =>
            println!("reticulate splines"),
            
        MyEnum::B { num } => 
            println!("rectify carborator #{}", num),
            
        _ => println!("other"),
    }
}

Pattern

Matching

Boolean

Conditions

match

if

if let

while

while let

enum MyEnum {
    A { num: u32 },
    B,
}

fn main() {
    let value = A { num: 22 };
    
    if let MyEnum::A { num } = value {
        println!("Variant A: {}", num);
    } else {
        println!("Other variant");
    }
}
while let SourceState::Item(item) = source.get_item() {
    println!("has item");
}
while source.should_continue() {
    println!("continuing");
}
let break_value = loop {
    if let Some(val) = get_item() {
        break val;
    }
};
  • Loops forever (until break'd)
  • Same as

while true

for <item> in <iterator> {
    <body>
}
  • Works with Iterators
  • For now, know it works with
    • lists (vectors)
    • ranges
    • more

Option and Panics

Option enum

enum Option<T> {
    Some(T),
    None,
}
  • std::option::Option - included in global namespace
    • Option, Some(T), None
  • ignoring Option gives compiler warning

C++'s

std::optional<T>

Rust C++
return None; return std::nullopt;
return Some(foo); return foo;
is_some() operator bool()
has_value()
unwrap() value()
unwrap_or(bar) value_or(bar) 
fn maybe_get_number() -> Option<u32> { [...] }

match maybe_get_number() {
    Some(num) => println!("Got number: {}", num),
    None => println!("Didn't get anything!"),
}

1. Match on Option

fn maybe_get_number() -> Option<u32> { [...] }

fn my_fun() -> Option<String> {
    let num = maybe_get_number()?;
    Ok(format!("Got number: {}", num))
}

2. Propagate Option using ? operator

fn maybe_get_number() -> Option<u32> { [...] }

let num = maybe_get_number().unwrap();
println!("Got number: {}", num);

3. Panic on None using unwrap

Panic

fn main() {
    panic!("something bad happened");
}
thread 'main' panicked at 'what is even going on', src/main.rs:2:5
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
enum Result<T, E> {
    Ok(T),
    Err(E),
}

Also Result

Like option, but contains error variant

Sometimes unwrapped

Often handled, will talk about later

Modules and Visibility

  • source file is compilation unit
  • namespaces
  • visibility
  • crate is compilation unit
  • modules
  • visibility
mod a_module {

  pub fn a_function() {}

}

use a_module::a_function;

fn main() {
    a_function();
}

src/main.rs

mod a_module;

use a_module::a_function;

fn main() {
    a_function();
}

src/main.rs

pub fn a_function() {}

src/a_module.rs

mod a_module;

use a_module::a_function;

fn main() {
    a_function();
}

src/main.rs

pub fn a_function() {}

src/a_module/mod.rs

pub fn a_function() {}

src/a_module/nested.rs

src/a_module/mod.rs

pub mod nested;

src/a_module/mod.rs

mod a_module;

use a_module::nested::a_function;
pub struct Counter {
    [...]
}

src/lib.rs

[dependencies]

# Depend on a crate on crates.io by version
rand = "0.8.4"

# Depend on a crate in a git repository
rand = { git = "https://github.com/rust-random/rand.git" }

# Depend on a local crate, by path
my_crate = { path = "../my_crate" }

Cargo.toml

Memory

Stack

Heap

Stack

Stack top

main

a

fn main() {
    let a = 1;
    let b = do_stuff(a);
}

fn do_stuff(m: u32) {
    [...]
}

do_stuff

m

deep_fun

...

Stack

Stack top

main

a

fn main() {
    let a = 1;
    let b = do_stuff(a);
}

fn do_stuff(m: u32) {
    [...]
}

do_stuff

m

Stack

Stack top

main

b, a

fn main() {
    let a = 1;
    let b = do_stuff(a);
}

fn do_stuff(m: u32) {
    [...]
}

Stack

Heap

Heap

Stack top

main

do_stuff

malloc()

my

string

0xa2

free()

Stack

Stack top

main

a

fn main() {
    let a = 1;
    let b = do_stuff(a);
}

fn do_stuff(m: u32) {
    [...]
}

do_stuff

m

deep_fun

...

Ownership

fn main() {
	
    let a_string = String::from("Hello, world!");
    
    println!("{:?}", a_string);

}
fn main() {
	
    {
        let a_string = String::from("Hello, world!");
    
        println!("{:?}", a_string);
    }

    // Not gonna work!
    // println!("{:?}", a_string);
}
fn main() {
	
    let string_a = String::from("Hello, world!");
    let string_b = string_a;
    
    println!("{:?}", string_a);
    println!("{:?}", string_b);

}
fn main() {
	
    let string_a = String::from("Hello, world!");
    let string_b = string_a;
    
    println!("{:?}", string_a);

}
error[E0382]: borrow of moved value: `string_a`
 --> src/main.rs:6:22
  |
3 |     let string_a = String::from("Hello, world!");
  |         -------- move occurs because `string_a` has type `String`, 
  |                  which does not implement the `Copy` trait
4 |     let string_b = string_a;
  |                    -------- value moved here
5 |     
6 |     println!("{:?}", string_a);
  |                      ^^^^^^^^ value borrowed here after move

cargo run

  • Each value in Rust has an owner
  • There can only be a single owner at a time
  • When the owner goes out of scope, the value will be dropped

The rules of the game

fn main() {
	
    let string_a = String::from("Hello, world!");
    let string_b = string_a;
    
    println!("{:?}", string_a);

}
ptr
len 13
capacity 13

String

H
e
l
l
o
,
w
o
r
l
d
!
fn my_fun(string: String) {
    println!("Hello, {}!", string);
}

fn main() {
    let string = String::from("world");
    
    my_fun(string);
    
    println!("Hello again, {}!", string);
}
error[E0382]: borrow of moved value: `string_a`
 --> src/main.rs:6:22
  |
3 |     let string_a = String::from("Hello, world!");
  |         -------- move occurs because `string_a` has type `String`, 
  |                  which does not implement the `Copy` trait
4 |     let string_b = string_a;
  |                    -------- value moved here
5 |     
6 |     println!("{:?}", string_a);
  |                      ^^^^^^^^ value borrowed here after move

cargo run

fn my_fun(string: String) {
    println!("Hello, {}!", string);
}

fn main() {
    let string = String::from("world");
    
    my_fun(string);
    
    println!("Hello again, {}!", string);
}

cargo run

error[E0382]: borrow of moved value: `string`
  --> src/main.rs:10:34
   |
6  |     let string = String::from("world");
   |         ------ move occurs because `string` has type `String`, 
                    which does not implement the `Copy` trait
7  |     
8  |     my_fun(string);
   |            ------ value moved here
9  |     
10 |     println!("Hello again, {}!", string);
   |                                  ^^^^^^ value borrowed here 
                                             after move

Clone

Copy

  • Performed implicitly by the compiler
  • Performed by straight memcpy
  • Performed explicitly by calling ------
  • Can have custom implementation

.clone()

fn main() {
	
    let string_a = String::from("Hello, world!");
    let string_b = string_a;
    
    println!("{:?}", string_a);
    println!("{:?}", string_b);

}
error[E0382]: borrow of moved value: `string_a`
 --> src/main.rs:6:22
  |
3 |     let string_a = String::from("Hello, world!");
  |         -------- move occurs because `string_a` has type `String`, 
  |                  which does not implement the `Copy` trait
4 |     let string_b = string_a;
  |                    -------- value moved here
5 |     
6 |     println!("{:?}", string_a);
  |                      ^^^^^^^^ value borrowed here after move

cargo run

fn main() {
	
    let string_a = String::from("Hello, world!");
    let string_b = string_a.clone();
    
    println!("{:?}", string_a);
    println!("{:?}", string_b);

}
$ cargo run
"Hello, world!"
"Hello, world!"

cargo run

#[derive(Copy, Clone)]
struct MyStruct {
    [...]
}
#[derive(Copy, Clone)]
struct MyStruct {
    my_string: String,
    my_integer: u32,
}

Borrowing & The Borrow Checker

The sequel of Ownership:

std::vector<int> myvector;
myvector.push_back(1);

int& num = myvector[0];
myvector.push_back(2);

std::cout << num << "\n";
let mut vec = Vec::new();
vec.push(1);

let num = &vec[0];
vec.push(2);

println!("{}", num);
std::vector<int> myvector;
myvector.push_back(1);

int& num = myvector[0];
myvector.push_back(2);

std::cout << num << "\n";
let mut vec = Vec::new();
vec.push(1);

let num = &vec[0];
vec.push(2);

println!("{}", num);
error[E0502]: cannot borrow `vec` as mutable because it 
              is also borrowed as immutable
 --> src/main.rs:6:1
  |
5 | let num = &vec[0];
  |            --- immutable borrow occurs here
6 | vec.push(2);
  | ^^^^^^^^^^^ mutable borrow occurs here
7 | 
8 | println!("{}", num);
  |                --- immutable borrow later used here
fn print_string(string: &String) {
    println!("{}", string);
}

fn main() {
    let my_string = String::from("hello");
    print_string(&string);
    print_string(&string);
}
fn append_newline(string: &String) {
    string.push_str("\n");
}

fn main() {
    let my_string = String::from("hello");
    append_newline(&my_string);
    println!("{:?}", my_string);
}

cargo run

error[E0596]: cannot borrow `*string` as mutable, as it is behind a `&` 
              reference
 --> src/main.rs:2:5
  |
1 | fn append_newline(string: &String) {
  |                           ------- help: consider changing this to be 
                                      a mutable reference: `&mut String`
2 |     string.push_str("\n");
  |     ^^^^^^ `string` is a `&` reference, so the data it refers to 
               cannot be borrowed as mutable
fn append_newline(string: &String) {
    string.push_str("\n");
}

fn main() {
    let my_string = String::from("hello");
    append_newline(&my_string);
    println!("{:?}", my_string);
}

cargo run

error[E0596]: cannot borrow `*string` as mutable, as it is behind a `&` 
              reference
 --> src/main.rs:2:5
  |
1 | fn append_newline(string: &String) {
  |                           ------- help: consider changing this to be 
                                      a mutable reference: `&mut String`
2 |     string.push_str("\n");
  |     ^^^^^^ `string` is a `&` reference, so the data it refers to 
               cannot be borrowed as mutable

&_

&mut _

  • several may exist for a single piece of data
  • may be copied
  • may only be read
  • only ONE may exist for any single piece of data
  • may only be moved
  • may be written or read

Mutually exclusive!

fn append_newline(string: &String) {
    string.push_str("\n");
}

fn main() {
    let my_string = String::from("hello");
    append_newline(&my_string);
    println!("{:?}", my_string);
}

cargo run

error[E0596]: cannot borrow `*string` as mutable, as it is behind a `&` 
              reference
 --> src/main.rs:2:5
  |
1 | fn append_newline(string: &String) {
  |                           ------- help: consider changing this to be 
                                      a mutable reference: `&mut String`
2 |     string.push_str("\n");
  |     ^^^^^^ `string` is a `&` reference, so the data it refers to 
               cannot be borrowed as mutable
fn append_newline(string: &mut String) {
    string.push_str("\n");
}

fn main() {
    let my_string = String::from("hello");
    append_newline(&my_string);
    println!("{:?}", my_string);
}

cargo run

error[E0308]: mismatched types
 --> src/main.rs:7:20
  |
7 |     append_newline(&my_string);
  |                    ^^^^^^^^^^ types differ in mutability
  |
  = note: expected mutable reference `&mut String`
                     found reference `&String`
fn append_newline(string: &mut String) {
    string.push_str("\n");
}

fn main() {
    let my_string = String::from("hello");
    append_newline(&mut my_string);
    println!("{:?}", my_string);
}

cargo run

error[E0596]: cannot borrow `my_string` as mutable, as it is 
              not declared as mutable
 --> src/main.rs:7:20
  |
6 |     let my_string = String::from("hello");
  |         --------- help: consider changing this to be 
                            mutable: `mut my_string`
7 |     append_newline(&mut my_string);
  |                    ^^^^^^^^^^^^^^ cannot borrow as mutable
fn append_newline(string: &mut String) {
    string.push_str("\n");
}

fn main() {
    let mut my_string = String::from("hello");
    append_newline(&mut my_string);
    println!("{:?}", my_string);
}

cargo run

"hello\n"
fn main() {
    let mut my_string = String::from("abc");
    
    let ref_a = &mut my_string;
    let ref_b = &my_string;
    
    println!("{} {}", ref_a, ref_b);
}

cargo run

error[E0502]: cannot borrow `my_string` as immutable because 
              it is also borrowed as mutable
 --> src/main.rs:5:17
  |
4 |     let ref_a = &mut my_string;
  |                 -------------- mutable borrow occurs here
5 |     let ref_b = &my_string;
  |                 ^^^^^^^^^^ immutable borrow occurs here
6 |     
7 |     println!("{} {}", ref_a, ref_b);
  |                       ----- mutable borrow later used here

cargo run

error[E0502]: cannot borrow `my_string` as immutable because 
              it is also borrowed as mutable
 --> src/main.rs:5:17
  |
4 |     let ref_a = &mut my_string;
  |                 -------------- mutable borrow occurs here
5 |     let ref_b = &my_string;
  |                 ^^^^^^^^^^ immutable borrow occurs here
6 |     
7 |     println!("{} {}", ref_a, ref_b);
  |                       ----- mutable borrow later used here
fn main() {
    let mut my_string = String::from("abc");
    
    let ref_a = &mut my_string;
    let ref_b = &my_string;
    
    println!("{} {}", ref_a, ref_b);
}
fn main() {
    let mut my_string = String::from("abc");
    
    let ref_a = &mut my_string;
    println!("{}", ref_a);
    
    let ref_b = &my_string;
    println!("{}", ref_b);
    
    // ref_a and ref_b are both still in scope
}
$ cargo run
abc
abc
let mut a = 0;

let a_ref = &mut a;
*a_ref = 1;

println!(a);

Dereferencing

let a = 12;
let a_ref = &a;

let a2 = *a_ref;

Rust for C++ Developers - Itema Day 1

By Hans Elias Bukholm Josephsen

Rust for C++ Developers - Itema Day 1

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