Rust

Terms

• • Fat Pointer Contains Address actual data and length

Cargo

Sample file

[package]
name = "hello_world"
version = "0.0.1"
authors = [ "Iain Wiseman iwiseman@bibble.co.nz" ]

Sample commands

 cargo new hello_world --bin
 cargo build
 cargo run

Fundamental Data Types

Primitive types

Cam declare with size of type

 let a:u8 = 123; // unsigned int 8 bits number immutable
 let a:i8 = 123; // signed int 8 bits number immutable
 let mut a:u8 = 123; // unsigned int 8 bits number mutable

Or without e.g.

 let mut c = 123456789 // 32-bit signed i32
 println!("c = {}", c);

Now variable based on OS e.g.

 let z:isize = 123 // signed 64 bit if on 64 bit OS

Decimal

let e:f64 = 2.5 // double-precision, 8 bytes or 64-bits

Char

let x:char = 'x' // Note 4 bytes unicode

boolean

let g:bool = false; // Note 4 bytes unicode

Operators

Does not support -- and ++ but does support

a -= 2;

Remainder can be calculated using

a%3

Bitwise

let c = 1 | 2 // | OR

Shift

let two_to_10 = 1 << 10; // 1024

Logical of standard e.g.

let pi_less_4 = std::f64::consts::PI < 4.0; // true

Scope and shadowing

Curly braces keep scope

 fn test()
 {
   {
     let a = 5; 
   }
   println!("Broken {a}");
 }

Shadowing is fine though

 fn test()
 {
   let a = 5; 
   {
     let a = 10; 
     println!("10 {a}");
   }
   println!("5 {a}");
 }

Constants

Standard const

 const MEANING_OF_LIFE:u8 = 42;

Static const

 static Z:i32 = 123;

Stack and Heap

Same a c++ i.e.

 let y = Box::new(10);
 println!("y = {}", *y);

Types

Tuples

Eezy peezy lemon squeezy

fn sum_and_product(x:i32,y:i32) -> (i32, i32)
{
 (x+y, x*y)
}

fn main()
{
  let sp = sum_and_product(3,4);
  let (a,b) = sp;
  let sp2 = sum_and_product(4,5);
   
  // combine
  let combined = (sp, sp2);
  let ((c,d), (e,f)) = combined;
}

Arrays

Array sizes cannot grow in rust

Simple

let mut a:[i32;5] = [1,2,3,4,5];
// Or 
let mut a = [1,2,3,4,5];
// Length
 a.len()
// Assignment
 a[0] = 321
// Printing
 println!("{:?}", )
// Testing
  if a == [1,2,3,4,5]
  {
  }
// Initialise
  let b = [1,10]; // 10 array initialised to 1

Multi Dimension

Here is a two dimension array

let mtx:[[f32;3];2] =
[
  [1.0, 0.0, 0.0],
  [0.0, 2.0, 0.0],
];

Slices

A slice is a non-owning pointer to a block of memory. For example

// Create a vector
let v: Vec<i32> = {0..5}.collect();

// Now create a slice (reference)
let sv: &[i32]= &v;

// We create a slice with only some elements
let sv1: &[i32]= &v[2..4];

// Printing these will produce the same result
println!("{:?}",v);
println!("{:?}",sv);

// And the range
println!("{:?}",sv1);

Get the first 3 elements of an array

fn use_slice(slice: &mut[i32])
{

}

fn test()
{
  let mut data = [1,2,3,4,5];
  // Passes element 1-3 to use_slice as a reference
  use_slice( &mut data[1..4]); 
}

Strings

Basic String

let name = String::from("Iain");

Two types, static string and string type

let s = "hello";
// Cannot do
// let h = s[0]
// You can iterate as a sequence using chars e.g.
for c in s.chars()
{
  println!("{}", c);
}

And now the mutable string in rust essentially an vector // Create a string

let mut letters = String::new();

Add a char

let a = 'a' as u8;
letters.push(a as char);

String to str

let u:%str = &letters;

Concatenation

let z = lettters + &letters

Other examples

let mut abc = "hello world".to_string()'
abc.remove(0);
abc.push_str("!!!");
abc.replace("ello","goodbye")

Hashmap

Reminds me of my C++ and Java days. No surprises here for reference

let mut basket = HashMap::new();

basket.insert(String::from("banana"), 2);
basket.insert(String::from("pear"), 2);
basket.insert(String::from("peach"), 2);

Updating was a bit more tricky than expected. This was the copilot approach

struct TeamScores {
    goals_scored: u8,
    goals_conceded: u8,
}

fn build_scores_table(results: &str) -> HashMap<&str, TeamScores> {
    // The name of the team is the key and its associated struct is the value.
    let mut scores = HashMap::new();

    for line in results.lines() {
        let mut split_iterator = line.split(',');
        // NOTE: We use `unwrap` because we didn't deal with error handling yet.
        let team_1_name = split_iterator.next().unwrap();
        let team_2_name = split_iterator.next().unwrap();
        let team_1_score: u8 = split_iterator.next().unwrap().parse().unwrap();
        let team_2_score: u8 = split_iterator.next().unwrap().parse().unwrap();

        // TODO: Populate the scores table with the extracted details.
        // Keep in mind that goals scored by team 1 will be the number of goals
        // conceded by team 2. Similarly, goals scored by team 2 will be the
        // number of goals conceded by team 1.
        let team_1 = scores.entry(team_1_name).or_insert(TeamScores::default());
        team_1.goals_scored += team_1_score;
        team_1.goals_conceded += team_2_score;

        let team_2 = scores.entry(team_2_name).or_insert(TeamScores::default());
        team_2.goals_scored += team_2_score;
        team_2.goals_conceded += team_1_score;
    }

    scores
}

The suggestion was to use get_mut on hashmap but struggle to get this to work. The solution from Chris biscardi on youtube was this, clearly the rust team looked at this and did it better.

fn build_scores_table(results: &str) -> HashMap<&str, TeamScores> {
...
        scores
            .entry(team_1_name)
            .and_modify(|team: &mut TeamScores| {
                team.goals_scored += team_1_score;
                team.goals_conceded += team_2_score;
            })
            .or_insert(TeamScores {
                goals_scored: team_1_score,
                goals_conceded: team_2_score,
            });

        scores
            .entry(team_2_name)
            .and_modify(|team: &mut TeamScores| {
                team.goals_scored += team_2_score;
                team.goals_conceded += team_1_score;
            })
            .or_insert(TeamScores {
                goals_scored: team_2_score,
                goals_conceded: team_1_score,
            });

Control Flow

if statement

Same as C++ except no brackets

 if temp > 30 
 {
    println!("Blah");
 }
 else if temp < 10 
 {
    println!("Blah"); 
 }
 else
 {
    println!("Blah"); 
 }

Elvis is like

  let a = if temp > 30 {"sunny"} else {"cloud"}

While and Loop

While

Same as C++ except no brackets

 while x < 1000
 {
 }

There is support for continue and break

Loop

Loop is while true

 loop
 {
    if y == 1 << 10 { break; }
 }

For Loop

A bit like kotlin loops (I think)

 for x in 1..11
 {
    println!("x = {}",x);
 }

You can get position in series as well

 for (pos,x) in (1..11).enumerate()
 {
    println!("x = {}, pos = {}",x, pos);
 }

Rust Principles

Move

Move is when you assign a value to another variable. If we try and use a variable after the move we will get an error.

let v = vec![1,2,3]
let v2 = v;
println!("{:?}",v2)
println!("{:?}",v) // Error

Copy

When we copy something me make a new thing. They is not the same a let a = b, which is assignment. Copy means we duplicate the underlying data of the type. For primitives a copy is implemented by default. This is because the primitive has a know size. E.g. u32, bool etc. If you want to be able to copy a non primitive you need to add the derive macro. Note Clone must also be specified

#[derive(Copy, Clone)]
enum Direction {
    North,
    East,
    South,
    West,
}

#[derive(Copy, Clone)]
struct RoadPoint {
    direction: Direction,
    index: i32,
}

Clone

Clone is a method you can call on a struct if you want a second instance and not move the ownership. Here is an example. The struct obviously needs to implement the Copy/Clone macro. Cloning clearly increases the memory used.

let v = vec![1,2,3]
let v2 = v.cone();
println!("{:?}",v)
println!("{:?}",v2)

References

So references are like C++ references, but for rust this means you can pass the ownership during function call

main() {
    let mut s = String::from("Hello");
    change_string(&mut s);
}

fn change_string(some_string: &mut String) {
    some_string.push_str(", world!");
}

Note for returning a Reference
If we are returning a reference we must be returning a parameter as all local variables are destroyed. (Clearly Rust is not going to allow new MyMemory(6502)

Structs

General

There are 3 types of structs, name, tuple and unit structs

• • Named
  • Tuples
  • Unit

Name Struct

struct User
{
  active: bool,
  username: String,
  sign_in_count: u32
}

let user1 = User{active: true, username: String::from("Biil"),
  sign_in_count: 0};
println!("{}", user1.username);

...

fn build_user(username: String) -> User {
   User {
     username,
     active:true,
     sign_in_count: 1
   }
}

Tuple Struct

Tuple structs use the order in which declared to assign.

   struct Coordinates{i32,i32,i32};
   let coords = Coordinates{1,2,3};

Unit Struct

These are used to mark the existence of something

struct UnitStruct;
let a = UnitStruct{}

The example shown was when you are implementing a trait (interface) but the properties were not required for this type. So given a trait for Area, Square uses size but Point does not have an area as it is zero

trait AreaCalculator {
  fn calc_area(&self) => f64
}

struct Square {
  size: f64
}

struct Point;

impl AreaCalculator for Square { 
  fn calc_area(&self) -> f64 {
    self.size * self.size
  } 
} 

impl AreaCalculator for Point { 
  fn calc_area(&self) -> f64 {
    0.0
  } 
}

We can use it for error

struct DivideByZero;

fn divide(nom: f64, den: f64) -> Result<f64, DivideByZero> {
   if den != 0.0 {
       Ok(nom/den)
   } else {
       Err(DivideByZero)
   }
}

Example Structs

struct Point
{
  x: f64,
  y: f64
}

fn main()
{
  let p = Point { x: 30.0, y: 4.0 };
  println!("point is at ({},{})", p.x, p.y)
}

Methods on Structs

Methods on struct require the first argument to be self

Example Method

Add method len to struct

struct Line
{
 start: Point,
 end: Point
}

// Declare impl using the keyword impl. Not ends with no semi colon.
impl Line
{
  fn len(&self) -> f64
  {
    let dx = self.start.x - self.end.x;
    let dy = self.start.y - self.end.y;
    (dx*dx+dy*dy).sqrt()
  }
}

Changing an attribute

To change an attribute and ensure you do not break the borrowing rules we do

struct Square {
   width: u32,
   height: u32
}

impl Square
{
  fn area(&self) -> u32 {
     self.width * self.height
  }

  fn change_width(&mut self, new_width: u32) -> Self
  {
    self.width = new_width;
  }
}

...
main() {
...
   let mut sq = Square(width:5, height: 5);
   sq.change_point(10) 
}

Lifetime

What are Dangling References

The code below will not compile. This is because x goes out of scope before r. I am guessing this is what is known as a dangling reference.

fn test() {
    let r;
    {
        let x = 5;
        r = &x; // Error `x` does not live long enough
    }
    log::info!("{}",r);
}

Lifetime Annotations

Not sure which way around these are but you specify lifetime annotations on functions and structs and they imply information to the compiler on how long the parameters will live for.

Three Rules of Lifetimes

Here are the rules but we also need to understand what they apply to. Kind of chicken and egg. An example is give below which is broken because these rules are not followed.

1. Each Parameter that is a reference gets its own lifetime parameter
2. If there is exactly one input lifetime parameter, that lifetime is assigned to all output lifetime parameters
3. If there are multiple input lifetime parameters, but one of them is &self or &mut self the lifetime is assigned to all output lifetime parameters

Example (Broken code)

Here is an example of code which cannot be compiled without lifetime being specified.

pub struct TestStruct {
    length: i32,
}

fn test2(x: &TestStruct, y: &TestStruct) -> &TestStruct { // Missing lifetime specifier
    if x.length > y.length {
      x
    }
    else {
      y 
    }
}

Adding Annotations

To do this we specify annotations. The extension in vscode does this for us using the quick fix. The code now looks like this

fn test2<'a>(x: &'a TestStruct, y: &'a TestStruct) -> &'a TestStruct {
    if x.length > y.length {
      x
    }
    else {
      y 
    }
}

My inference from this is that all parameters have the same lifetime.

Lifetime Annotations for Structs

Structs can also have lifetime annotations. If you specify a reference then you will need to specify a lifetime annotation. In the example below when we make the struct of type MyString we need to make sure that str1 does not go out of scope while x of type MyString exists otherwise it would refer to something no longer in scope.

// Without lifetime annotation will not compile.
// struct MyString {
//   text: &str,
// }


struct MyString<'a> {
  text: &'a str,
}

fn main() {

    let str1 = String::from("This is my String);
    let x = MyString(text: str1.as_str());
}

Static Lifetimes

We can also have lifetimes for statics.

let s: &'static str = "I live forever";

Doing this means the values are stored in the binary.

Enums

Example 1 with Method

Seems a bit C++ but...

enum Pet {dog, cat, fish}

And now lets add a method as we do with structs. Note for this method we are returning something and with rust all locals are destroyed on return so we need to specify a lifetime.

enum Pet {dog, cat, fish}

impl Pet {
   fn what_am_i(self) -> &'static str {
      match self {
         Pet::dog => "I am a dog", 
         Pet::cat => "I am a cat",
         Pet::fish => "I am a fish",   
      }
   }
}

Example 2

enum Color {
  Red,
  Green,
  Blue
}

fn main()
{
  let c:Color = Color::Red;
  match c
  {
     Color::Red => prinln!("Color is Red");
     Color::Green => prinln!("Color is Green");
  }
}

Example 3 with Types

enum Color {
  Red,
  Green,
  Blue,
  RgbColor(u8,u8,u8) // Tuple
  CmykColor{cyan:u8, magenta:u8, yellow:u8, black:u8,} // Struct
}

fn main()
{
  let c:Color = Color::RgbColor(10,0.0);
  match c
  {
     Color::Red => prinln!("Color is Red");
     Color::Green => prinln!("Color is Green");
     Color::RgbColor(0,0,0) => prinln!("Color is Black");
     Color::RgbColor(r,g,b) => prinln!("Color is {},{},{}", r,g,b);
  }

  let d:Color = Color::CmykColor(cyan:0, magenta:0, yellow:0, black:0);
  match d
  {
     Color::Red => prinln!("Color is Red");
     Color::Green => prinln!("Color is Green");
     Color::RgbColor(0,0,0) => prinln!("Color is Black");
     Color::CmykColor(cyan:_, magenta:_, yellow:_, black:255) => prinln!("Black");
  }
}

Option<T> Enum

This enum if provided for us by rust and looks like this

enum Option<T> {
    None,
    Some(T)
}

We would choose this type when we have a case where there could be a value or not. I guess this is the equivalent of string? in Typescript where we may or may not have a value. In rust we use match to support this type.

  let some_number = Some(5); 
  let some_string = Some("a string");
  let nothing: Option<i32> = None;

Pattern Matching

Match is Exhaustive approach to pattern matching. I.E. you need to specify something for every option you are using match for. However you can include a default. I find this a great approach

Examples

Simple Match

match x
{
  0 => "zero"
  1 | 2 => "one or two"
  9...11 => "lots of"  // two dots does not include end value (exclusive)
  _ if(blahh) => "something"
  _ => "all others"
}

Here is another example.

 let country = match country_code
 {
    44 => "uk",
    46 => "sweden",
    7 => "russia"
    1...999 => "unknown" // other triple dot does include end value (inclusive)
    _ => "invalid" // invalid
 };

This just shows inclusive which is ..= unlike kotlin which I think is 3 dots

// This function returns how much icecream there is left in the fridge.
// If it's before 22:00 (24-hour system), then 5 scoops are left. At 22:00,
// someone eats it all, so no icecream is left (value 0). Return `None` if
// `hour_of_day` is higher than 23.
fn maybe_icecream(hour_of_day: u16) -> Option<u16> {
    match hour_of_day {
        0..22 => Some(5),
        22..=23 => Some(0),
        _ => None,
    }
}

More Complex

Stumped me when see thing for the first time prior to type script and possibly lambda. Here we define anonymous functions which match the type of the enum. Here is the enum which is used in another struct

enum Message {
    Move(Point),
    Echo(String),
    ChangeColor(u8, u8, u8),
    Quit,
    Resize { width: u64, height: u64 },
}

It has functions for each enum type.

struct State {
    width: u64,
    height: u64,
    position: Point,
    message: String,
    // RGB color composed of red, green and blue.
    color: (u8, u8, u8),
    quit: bool,
}

impl State {
    fn resize(&mut self, width: u64, height: u64) {
        self.width = width;
        self.height = height;
    }

    fn move_position(&mut self, point: Point) {
        self.position = point;
    }

    fn echo(&mut self, s: String) {
        self.message = s;
    }

    fn change_color(&mut self, red: u8, green: u8, blue: u8) {
        self.color = (red, green, blue);
    }

    fn quit(&mut self) {
        self.quit = true;
    }

    fn process(&mut self, message: Message) {
...
    }
}

At first I struggled to understand how to implement process but all you need to do is provide an ()_=> {} for each type. For Quit I completely understood but for the others was confused. Obvious once you know and I am sure copilot will do this for me

    fn process(&mut self, message: Message) {
        match message {
            Message::Move(point) => self.move_position(point),
            Message::Echo(output) => self.echo(output),
            Message::ChangeColor(red, green, blue) => self.change_color(red, green, blue),
            Message::Quit => self.quit(),
            Message::Resize { width, height } => self.resize(width, height),
        }
    }

Match on Tuples

This is an exert from [Game of Life]. We can match on tuples, and I imagine other types too. For tuples you can specify a value or compare to a value. Note the use of otherwise

    let next_cell = match (cell, live_neighbors) {
      // Rule 1: Any live cell with fewer than two live neighbours
      // dies, as if caused by underpopulation.
      (Cell::Alive, x) if x < 2 => Cell::Dead,
      // Rule 2: Any live cell with two or three live neighbours
      // lives on to the next generation.
      (Cell::Alive, 2) | (Cell::Alive, 3) => Cell::Alive,
      // Rule 3: Any live cell with more than three live
      // neighbours dies, as if by overpopulation.
      (Cell::Alive, x) if x > 3 => Cell::Dead,
      // Rule 4: Any dead cell with exactly three live neighbours
      // becomes a live cell, as if by reproduction.
      (Cell::Dead, 3) => Cell::Alive,
      // All other cells remain in the same state.
      (otherwise, _) => otherwise,
};

Operators and Symbols

Found in Table B-1 here [Operators and Symbols]

1. [Range]: 1..10
2. [RangeFrom]: 1..
3. [RangeTo]: ..10
4. RangeFull: ..
5. RangeInclusive: 1..=10
6. RangeToInclusive: ..=10

Option <T> and if let

Used to avoid null or invalid values. This was used in things where the value might be present. Maybe command line arguments where some were provide or none were provided. Lets to the classic divide by zero.

let x = 3.0
let y = 0.0 // Divide by zero

let result:Option<f64> = 
   if y != 0.0 { Some(x/y) } else { None };

// Using match
match result {
   Some(z) => println!("Goody result"),
   None => println!("No result")
}

// Using if let
if let Some(z) = result { println!("z = {}", z); }

More if let

Here is another example

let mut stack = Vec:new();
stack.push(1);
stack.push(2);
stack.push(3);
while let Some(top) = stack.pop() {
   println!("{}", top);
}

while let

The above example makes great sense but while doing rustlings the was this question

  // TODO: Make this a while-let statement. Remember that `Vec::pop()`
  // adds another layer of `Option`. You can do nested pattern matching
  // in if-let and while-let statements.
  integer = optional_integers.pop() {
    assert_eq!(integer, cursor);
    cursor -= 1;
  }

I did like the Some Some approach

   while let Some(Some(integer)) = optional_integers.pop() {
     assert_eq!(integer, cursor);
     cursor -= 1;
   }

But could not get the You can do nested pattern matching in if-let and while-let statements to look nice

   while let Some(integer) = if let Some(integer) = optional_integers.pop() {
     integer
   } else {
     None
   } {
     assert_eq!(integer, cursor);
     cursor -= 1;
   }

Just wouldn't let it lie, found a way to turn it up the right way

   while let Some(integer) = optional_integers.pop() {
     if let Some(integer) = integer {
       assert_eq!(integer, cursor);
       cursor -= 1;
     }
   }

Generics

Simple

This is very similar to C++ Templates and TypeScript Generics

struct Point<T>
{
  x: T,
  y: T
}

fn generics()
{
  let a:Point<i32> = Point {x: 0, y: 4}
}

Using Implementation

Must the same, just need good examples and we a well away

struct Wrapper<T> {
    value: T,
}

impl<T> Wrapper<T> {
    fn new(value: T) -> Self {
        Wrapper { value }
    }
}

Traits

Traits are similar to interfaces in java and c#

Defining a Traits

trait Animal
{
  fn create(name:&'static str);

  fn name(&self) => &'static str;

  fn talk(&self)
  {
     println!("{} cannot talk",self.name()); 
  }
}

Implement a Trait

Here we create a struct which will implement out trait. Note we do not have to implement all functions if the trait provides a default implementation

Implement a Trait for Animal

struct Human
{
   name: &'static str;
}

impl Animal for Human
{
  fn create(name:&'static str) -> Human
  {
    Human{name: name}
  }

  fn name(&self) -> &'static str
  { 
     self.name
  }
  // override default
  fn talk(&self)
  {
     println!("{} can talk",self.name()); 
  }
}

Implement a Trait for Cat

Here we implement the Animal Trait for Cat

struct Cat
{
   name: &'static str;
}

// Implement interface
impl Animal for Cat
{
  fn create(name:&'static str) -> Cat
  {
    Cat{name: name}
  }

  fn name(&self) -> &'static str
  { 
     self.name
  }
  // override default
  fn talk(&self)
  {
     println!("{} says meeow",self.name()); 
  }
}


// Usage
let h:Human = Animal::create("John");
let c:Cat = Animal::create("John");

Default Trait and Spread

For a struct we can create a default for it. We can use a typescript like spread operator (although it must be last) for override these defaults

pub struct Circle {
    color: String,
    point: Point,
    radius: u16,
}

impl Circle {
    pub fn new(color: String, point: Point, radius: u16) -> Circle {
        Circle {
            color,
            point,
            radius,
        }
    }

    pub fn default_color(point: Point, radius: u16) -> Circle {
        Circle {
            point,
            radius,
            ..Default::default()
        }
    }
}

impl Default for Circle {
    fn default() -> Self {
        Circle {
            color: String::from("black"),
            point: Point::new(0, 0),
            radius: 0,
        }
    }
}

// Default Circle
let circle = Circle::default();

// Default Black Circle
let circle = Circle::default_color(Point::new(1, 1), 1);

Traits and Impl

To allow any struct which implements the trait we use the dyn keyword

trait Licensed {
    fn licensing_info(&self) -> String {
        "Default license".to_string()
    }
}

struct SomeSoftware;
struct OtherSoftware;

impl Licensed for SomeSoftware {}
impl Licensed for OtherSoftware {}

// TODO: Fix the compiler error by only changing the signature of this function.
fn compare_license_types(software1: impl Licensed, software2: impl Licensed) -> bool {
    software1.licensing_info() == software2.licensing_info()
}

// Now we can do this
compare_license_types(SomeSoftware, OtherSoftware)
compare_license_types(OtherSoftware, SomeSoftware)

Provided Traits

Drop Trait

Drop trait is called automatically to free up resources but you can write your own e.g. for the example above we could write

impl Drop for Course {
  fn drop(&mut self) {
     println("Dropping")
  }
}

Clone Trait

Like the drop trait we can implement our own. Refer to the clone trait for this.

Copy Trait

We can either specify #[derive(Copy, Clone)] or implement our own. There are restrictions on this

From and Into Trait

This allow us to convert from one type to another

fn into(self) -> T
fn from(T) ->  Self
fn try_into(self) -> Result<T, Self: Error>
fn try_from(value: T) -> Result<Self, Self: Error>

Trait Bounds 1

In order to allow use of more than on trait in a function we can use the +. This example means that item must implement both traits, i.e. SomeTrait and OtherTrait

fn some_func(item: impl SomeTrait + OtherTrait) -> bool {
    item.some_function() && item.other_function()
}

Trait Bounds 2

Here is an example of doing the same thing in two ways. Because we can have anything in grade (T) we must make an implementation for std::fmt::Display. That way if we make a ReportCard with a generic which does not support Display, it will not compile

struct ReportCard<T> {
    grade: T,
    student_name: String,
    student_age: u8,
}

// Approach 1
impl<T> ReportCard<T>
where
    T: std::fmt::Display,
{
    fn print(&self) -> String {
        format!(
            "{} ({}) - achieved a grade of {}",
            &self.student_name, &self.student_age, &self.grade,
        )
    }
}

// Approach 2
impl<T: std::fmt::Display> ReportCard<T> {
    fn print(&self) -> String {
        format!(
            "{} ({}) - achieved a grade of {}",
             &self.student_name, &self.student_age, &self.grade,
        )
    }
}

Trait Bounds

The example above has two ways to achieve the same thing. If we constrain what this allowed, this is called trait bounds. Lets add a second parameter.

// This example only forces the struct to implement the trait
// fn overview(item1: &imp Overview, item2: &imp Overview) 

// But this force the struct to be of the same type
// fn overview<T: Overview>(item1: &T, item2: &T)

We can add more constraints with the + operator. Now they need the second trait.

// fn overview(item1: &imp Overview + AnotherTrait, item2: &imp Overview + AnotherTrait) 
// fn overview<T: Overview + AnotherTrait>(item1: &T, item2: &T)

Here we have an example of ensuring that the incoming parameters are constrained to be of type T

struct Pointy<T> {
    x: T,
    y: T,
}

impl <T> Add for Pointy <T>
where T: Add<Output = T>
{
    type Output = Self;

    fn add(self, other: Self) -> Self {
        Self {
            x: self.x + other.x, 
            y: self.y + other.y,
        }
    }
}

Passing Trait as Parameters

So here is an example of two structs with overview implement,one using the trait default implementation, the other its own. We can use the trait similar to a pointer to a function.

Example

trait Overview {
  fn overview(&self) -> String {
     format("This is a rust course")
  } 
}

struct Course {
  headline: String,
  author: String
}

struct AnotherCourse {
  headline: String,
  author: String
}

impl Overview for Course {
}

impl Overview for AnotherCourse {
  fn overview(&self) -> String {
     format("{}, {}", self.author, self.headline)
  } 
}

We can use the overview trait a a fn parameter with

fn call_overview(item: &imp) {
   println("Overview: {}", item.overview())
}

// OR 
fn call_overview<T: Overview>(item: &T) {
   println("Overview: {}", item.overview())
}

Passing Traits (From Youtube)

Taken from Youtube and repeated. There are two notations for passing a trait. These are the same but the first is perhaps more readable. The second is known as a trait bound.

pub fn foo (traitor: &impl SpiDevice) {

}

pub fn foo<T: SpiDevice>(traitor: &T) {

}

With the impl syntax we can make the parameter have more the one trait with a plus.

pub fn foo (traitor: &impl SpiDevice + AnotherTrait) {

}

With the second syntax if we have two parameters if allows us to make sure they both share the same trait easily as the type is only specified once

pub fn foo<T: SpiDevice>(traitor1: &T, traitor2) {

}

We can also add a second trait with this syntax too.

pub fn foo<T: SpiDevice + AnotherTrait>(traitor1: &T, traitor2) {

}

This starts to get messy to we can tidy this up with the Where Clause

pub fn foo<T, U>(traitor1: &T, traitor2: &U) -> i32
where 
    T: SpiDevice + AnotherTrait,
    U: AnotherTrait + YetAnotherTrait
        {
            42
        }

Returning Traits (From Youtube)

We can also return traits but you cannot return different types which share the same trait at this time.

pub fn foo() -> SpiDevice {
    // Must be of same type
}

Common Collections

Vectors

Same a c++

let mut a = Vec::new()
a.push(1);
a.push(2);
a.push(3);
// Print
println!("a[0] {}", a[0]);

// We can create vector with initial capacity
let mut b = Vec::<i32>::with_capacity(2);

// We can initialize using an iterator values of 0-4
let c: Vect<i32> = (0..5).collect();

// Using get returns a option
match a.get(3333)
{
...
}

// Removing, pop returns an option   
let last_elem = a.pop();

// Using the option type iterating over vector to print it
while let Some(x) = a.pop()
{
   println!("x = {}",x);
}

Binary Heap

This make sure the highest is at the top. It has a peek function to allow you to peek at values.

let mut bHeap = BinaryHeap::new();
bHeap.push(1);
bHeap.push(18);
bHeap.push(20);
bHeap.push(5);
bHeap.pop();

println!("{:?}", bHeap); // 20

Maps

Not discussed

Sets

Not discussed

Error Handling

Panic

Panic happens when unhandled error occurs. This happens for instance when we access out of bounds array. We can get a backtrace by setting the environment export RUST_BACKTRACE=-1

Result Enum

The Result an enum which has two generics Result<T, E> where T is the type an E is the error. In rust we use the match to determine what to do.

let file = File::Open("Does_not_exist.mp3");
let file match file {
    Ok(file) => file,
    Err(error) => panic("Error: {:?}", error),
};

Mapping Errors

Rust likes you to make your own errors and map the ones you handle to you errors which makes sense. We make our own errors using enums

enum ParsePosNonzeroError {
    Creation(CreationError),
    ParseInt(ParseIntError),
}

Now we can provide helper function to convert from one type of error to ours

impl ParsePosNonzeroError {
    fn from_creation(err: CreationError) -> Self {
        Self::Creation(err)
    }

    // TODO: Add another error conversion function here.
    fn from_parse_int(err: ParseIntError) -> Self {
        Self::ParseInt(err)
    }
}

Now in our parse function we can map the errors in parse() to our own

#[derive(PartialEq, Debug)]
struct PositiveNonzeroInteger(u64);

impl PositiveNonzeroInteger {
    fn new(value: i64) -> Result<Self, CreationError> {
        match value {
            x if x < 0 => Err(CreationError::Negative),
            0 => Err(CreationError::Zero),
            x => Ok(Self(x as u64)),
        }
    }

    fn parse(s: &str) -> Result<Self, ParsePosNonzeroError> {
        // TODO: change this to return an appropriate error instead of panicking
        // when `parse()` returns an error.
        let x: i64 = s.parse().map_err(ParsePosNonzeroError::from_parse_int)?;
        Self::new(x).map_err(ParsePosNonzeroError::from_creation)
    }
}

Testing

We specify the cfg option and use the assert library

fn sqrt(number: f64) -> Result<f64, String> {
    if number >= 0.0 {
        Ok(number.powf(0.5))
    } else {
        Err("negative floats don't have square roots".to_owned())
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_sqrt() -> Result<(), String> {
        let x = 4.0;
        assert_eq!(sqrt(x)?.powf(2.0), x);
        Ok(())
    }
}

We can run these with

cargo test

Handling CLI Arguments

Clap seems to be the approach for this, make sure you install the macros otherwise errors will show on the derive macro.

Closures

Closures are functions you which you can use the available scope to with that function. They look like anonymous function in typescript

Mapper Function using Closure

let a = 10;

let a = 10;

let a = 10;

Here is a closure which is like typescript mapper function using closures and rust