Premier League’s Return: A Hat Trick of Cyberthreats?

The beautiful game is back on the pitch in the U.K. — and cyberattackers will be looking to take advantage of fans streaming the games.

England’s Premier League is returning this week, with millions of soccer fans around the world looking to stream matches using their online video accounts. Unfortunately, the U.K.’s National Cyber Security Centre (NCSC) is warning on phishing, fraud and brute-forcing attempts by attackers looking to break into those accounts.

The organization said in a Wednesday announcement that it expects a rash of phishing, scam and account-takeover efforts centered around the return of the country’s most popular sport — a kind of hat trick of attack types. The assessment, it said, is based on precedent: The NCSC has also observed escalating cyberattacks on television streaming subscriptions as more and more people quarantine at home during the COVID-19 pandemic.

“As well as illegally watching the game the victim has paid for, the hackers could make unauthorized purchases on the platform or look to find personal information that could be used for further scams – including targeting them with scam emails or phone calls,” the organization warned.

#cloud security #web security #premier league #soccer #security

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Premier League’s Return: A Hat Trick of Cyberthreats?
Ray  Patel

Ray Patel

1619518440

top 30 Python Tips and Tricks for Beginners

Welcome to my Blog , In this article, you are going to learn the top 10 python tips and tricks.

1) swap two numbers.

2) Reversing a string in Python.

3) Create a single string from all the elements in list.

4) Chaining Of Comparison Operators.

5) Print The File Path Of Imported Modules.

6) Return Multiple Values From Functions.

7) Find The Most Frequent Value In A List.

8) Check The Memory Usage Of An Object.

#python #python hacks tricks #python learning tips #python programming tricks #python tips #python tips and tricks #python tips and tricks advanced #python tips and tricks for beginners #python tips tricks and techniques #python tutorial #tips and tricks in python #tips to learn python #top 30 python tips and tricks for beginners

Premier League’s Return: A Hat Trick of Cyberthreats?

The beautiful game is back on the pitch in the U.K. — and cyberattackers will be looking to take advantage of fans streaming the games.

England’s Premier League is returning this week, with millions of soccer fans around the world looking to stream matches using their online video accounts. Unfortunately, the U.K.’s National Cyber Security Centre (NCSC) is warning on phishing, fraud and brute-forcing attempts by attackers looking to break into those accounts.

The organization said in a Wednesday announcement that it expects a rash of phishing, scam and account-takeover efforts centered around the return of the country’s most popular sport — a kind of hat trick of attack types. The assessment, it said, is based on precedent: The NCSC has also observed escalating cyberattacks on television streaming subscriptions as more and more people quarantine at home during the COVID-19 pandemic.

“As well as illegally watching the game the victim has paid for, the hackers could make unauthorized purchases on the platform or look to find personal information that could be used for further scams – including targeting them with scam emails or phone calls,” the organization warned.

#cloud security #web security #premier league #soccer #security

Why the Premiere League is not the Best League

As a soccer fan you can hear it everywhere “Home of the best league: The premier league”, “The best league in the world is the premier league” … . Many people, but also professionals such as journalists and commentators regard the premier league as the best league in the world.

As a follower of both international UEFA leagues (Champions League and Euro League) I was confused about these statements. In my opinion, it was not clear which league is the best in the world and I would rather say it varies from year to year. The first thing I did to find it out was to look at the overall international titles that the various countries gathered. In the following, I only regard four leagues: Serie ABundesligaLaLiga, and Premier League. If you are into soccer, you might know why only these four leagues are considered. Taking a look at all titles and finalists in the last 10 to 20 years these four leagues represent above 90% of all titleholders and finalists.

Taking a look at the graphic below its obvious that the Spanish league LaLiga is by far the most successful league with a total of 30 titles. In this statistic the Bundesliga of my home country Germany is far behind at the end with only 14 titles. The premier league is in the middle with 22 titles close to Italy with 21 titles.

Image for post

#fifa #python #soccer #champions-league #premier-league

What we learned shifting Red Hat’s premier event

“Learn to pivot” has been the mantra for 2020. Like most businesses, March 2020 was a challenging time for us on the Red Hat marketing team. With COVID-19 spreading across the world, and businesses sending their employees to work from home, it became clear that Red Hat Summit, scheduled to be hosted in April in San Francisco, could not go on as planned.

By mid-March we were in full pivot mode to change Red Hat Summit, the premier open source technology conference, from an in-person event to a full digital experience. The challenge – that the event would still immerse our attendees in everything that makes a Red Hat event special. It was certainly an exciting ride, and on April 27, we opened the Summit virtual experience to the world. In the end, we had more than 50,000 attendees from more than 100 countries visit the live environment. We learned a lot of lessons along the way - below are a few successes we had while pulling off this event, and a one tip for improving a virtual experience.

Success #1: Be authentic to your brand

Red Hat has a unique, open culture that is at the heart of everything we do as an organization, and we try to make sure that culture is well-represented in our events. While shifting to a virtual event environment, we knew we needed to keep that Red Hat community feel, even though we wouldn’t be in person. That meant following some of the same guidelines we’d use for an in-person event, including:

  • Give attendees access to Red Hatters: At a live event, you’d do this in booths and one on one meetings. In our virtual events, we did this through chat rooms and “ask the experts” live sessions.

  • Make customers the star of the show: Red Hat products enable our customer to do some amazing things, and just like at a live Summit, we showcased their successes through customer keynotes, breakout sessions and our Red Hat Innovation Awards program.

  • Keep things fun: There’s always a lot to do at Summit, beyond attending keynotes and breakout sessions. We added open source games, challenges for completing tasks in the environment and opportunities to win prizes to the virtual experience to bring some of the excitement of Summit into attendees’ homes.

  • We were surprised at how well the gamification of the environment worked for helping with engagement numbers. Over 26,000 attendees earned at least one badge for watching keynotes, exploring the environment, and interacting with content from programs like Red Hat Innovation Awards.

#red hat’s #machine-learning #red hat innovation awards program.

Rust  Language

Rust Language

1636360749

Std Library Types in Rust - The Rust Programming Language

Std Library Types - Rust By Example

The std library provides many custom types which expands drastically on the primitives. Some of these include:

  • growable Strings like: "hello world"
  • growable vectors: [1, 2, 3]
  • optional types: Option<i32>
  • error handling types: Result<i32, i32>
  • heap allocated pointers: Box<i32>

Box, stack and heap

All values in Rust are stack allocated by default. Values can be boxed (allocated on the heap) by creating a Box<T>. A box is a smart pointer to a heap allocated value of type T. When a box goes out of scope, its destructor is called, the inner object is destroyed, and the memory on the heap is freed.

Boxed values can be dereferenced using the * operator; this removes one layer of indirection.

use std::mem;

#[allow(dead_code)]
#[derive(Debug, Clone, Copy)]
struct Point {
    x: f64,
    y: f64,
}

// A Rectangle can be specified by where its top left and bottom right 
// corners are in space
#[allow(dead_code)]
struct Rectangle {
    top_left: Point,
    bottom_right: Point,
}

fn origin() -> Point {
    Point { x: 0.0, y: 0.0 }
}

fn boxed_origin() -> Box<Point> {
    // Allocate this point on the heap, and return a pointer to it
    Box::new(Point { x: 0.0, y: 0.0 })
}

fn main() {
    // (all the type annotations are superfluous)
    // Stack allocated variables
    let point: Point = origin();
    let rectangle: Rectangle = Rectangle {
        top_left: origin(),
        bottom_right: Point { x: 3.0, y: -4.0 }
    };

    // Heap allocated rectangle
    let boxed_rectangle: Box<Rectangle> = Box::new(Rectangle {
        top_left: origin(),
        bottom_right: Point { x: 3.0, y: -4.0 },
    });

    // The output of functions can be boxed
    let boxed_point: Box<Point> = Box::new(origin());

    // Double indirection
    let box_in_a_box: Box<Box<Point>> = Box::new(boxed_origin());

    println!("Point occupies {} bytes on the stack",
             mem::size_of_val(&point));
    println!("Rectangle occupies {} bytes on the stack",
             mem::size_of_val(&rectangle));

    // box size == pointer size
    println!("Boxed point occupies {} bytes on the stack",
             mem::size_of_val(&boxed_point));
    println!("Boxed rectangle occupies {} bytes on the stack",
             mem::size_of_val(&boxed_rectangle));
    println!("Boxed box occupies {} bytes on the stack",
             mem::size_of_val(&box_in_a_box));

    // Copy the data contained in `boxed_point` into `unboxed_point`
    let unboxed_point: Point = *boxed_point;
    println!("Unboxed point occupies {} bytes on the stack",
             mem::size_of_val(&unboxed_point));
}

Vectors

Vectors are re-sizable arrays. Like slices, their size is not known at compile time, but they can grow or shrink at any time. A vector is represented using 3 parameters:

  • pointer to the data
  • length
  • capacity

The capacity indicates how much memory is reserved for the vector. The vector can grow as long as the length is smaller than the capacity. When this threshold needs to be surpassed, the vector is reallocated with a larger capacity.

fn main() {
    // Iterators can be collected into vectors
    let collected_iterator: Vec<i32> = (0..10).collect();
    println!("Collected (0..10) into: {:?}", collected_iterator);

    // The `vec!` macro can be used to initialize a vector
    let mut xs = vec![1i32, 2, 3];
    println!("Initial vector: {:?}", xs);

    // Insert new element at the end of the vector
    println!("Push 4 into the vector");
    xs.push(4);
    println!("Vector: {:?}", xs);

    // Error! Immutable vectors can't grow
    collected_iterator.push(0);
    // FIXME ^ Comment out this line

    // The `len` method yields the number of elements currently stored in a vector
    println!("Vector length: {}", xs.len());

    // Indexing is done using the square brackets (indexing starts at 0)
    println!("Second element: {}", xs[1]);

    // `pop` removes the last element from the vector and returns it
    println!("Pop last element: {:?}", xs.pop());

    // Out of bounds indexing yields a panic
    println!("Fourth element: {}", xs[3]);
    // FIXME ^ Comment out this line

    // `Vector`s can be easily iterated over
    println!("Contents of xs:");
    for x in xs.iter() {
        println!("> {}", x);
    }

    // A `Vector` can also be iterated over while the iteration
    // count is enumerated in a separate variable (`i`)
    for (i, x) in xs.iter().enumerate() {
        println!("In position {} we have value {}", i, x);
    }

    // Thanks to `iter_mut`, mutable `Vector`s can also be iterated
    // over in a way that allows modifying each value
    for x in xs.iter_mut() {
        *x *= 3;
    }
    println!("Updated vector: {:?}", xs);
}

More Vec methods can be found under the std::vec module


Strings

There are two types of strings in Rust: String and &str.

A String is stored as a vector of bytes (Vec<u8>), but guaranteed to always be a valid UTF-8 sequence. String is heap allocated, growable and not null terminated.

&str is a slice (&[u8]) that always points to a valid UTF-8 sequence, and can be used to view into a String, just like &[T] is a view into Vec<T>.

fn main() {
    // (all the type annotations are superfluous)
    // A reference to a string allocated in read only memory
    let pangram: &'static str = "the quick brown fox jumps over the lazy dog";
    println!("Pangram: {}", pangram);

    // Iterate over words in reverse, no new string is allocated
    println!("Words in reverse");
    for word in pangram.split_whitespace().rev() {
        println!("> {}", word);
    }

    // Copy chars into a vector, sort and remove duplicates
    let mut chars: Vec<char> = pangram.chars().collect();
    chars.sort();
    chars.dedup();

    // Create an empty and growable `String`
    let mut string = String::new();
    for c in chars {
        // Insert a char at the end of string
        string.push(c);
        // Insert a string at the end of string
        string.push_str(", ");
    }

    // The trimmed string is a slice to the original string, hence no new
    // allocation is performed
    let chars_to_trim: &[char] = &[' ', ','];
    let trimmed_str: &str = string.trim_matches(chars_to_trim);
    println!("Used characters: {}", trimmed_str);

    // Heap allocate a string
    let alice = String::from("I like dogs");
    // Allocate new memory and store the modified string there
    let bob: String = alice.replace("dog", "cat");

    println!("Alice says: {}", alice);
    println!("Bob says: {}", bob);
}

More str/String methods can be found under the std::str and std::string modules

Literals and escapes

There are multiple ways to write string literals with special characters in them. All result in a similar &str so it's best to use the form that is the most convenient to write. Similarly there are multiple ways to write byte string literals, which all result in &[u8; N].

Generally special characters are escaped with a backslash character: \. This way you can add any character to your string, even unprintable ones and ones that you don't know how to type. If you want a literal backslash, escape it with another one: \\

String or character literal delimiters occuring within a literal must be escaped: "\"", '\''.

fn main() {
    // You can use escapes to write bytes by their hexadecimal values...
    let byte_escape = "I'm writing \x52\x75\x73\x74!";
    println!("What are you doing\x3F (\\x3F means ?) {}", byte_escape);

    // ...or Unicode code points.
    let unicode_codepoint = "\u{211D}";
    let character_name = "\"DOUBLE-STRUCK CAPITAL R\"";

    println!("Unicode character {} (U+211D) is called {}",
                unicode_codepoint, character_name );


    let long_string = "String literals
                        can span multiple lines.
                        The linebreak and indentation here ->\
                        <- can be escaped too!";
    println!("{}", long_string);
}

Sometimes there are just too many characters that need to be escaped or it's just much more convenient to write a string out as-is. This is where raw string literals come into play.

fn main() {
    let raw_str = r"Escapes don't work here: \x3F \u{211D}";
    println!("{}", raw_str);

    // If you need quotes in a raw string, add a pair of #s
    let quotes = r#"And then I said: "There is no escape!""#;
    println!("{}", quotes);

    // If you need "# in your string, just use more #s in the delimiter.
    // There is no limit for the number of #s you can use.
    let longer_delimiter = r###"A string with "# in it. And even "##!"###;
    println!("{}", longer_delimiter);
}

Want a string that's not UTF-8? (Remember, str and String must be valid UTF-8). Or maybe you want an array of bytes that's mostly text? Byte strings to the rescue!

use std::str;

fn main() {
    // Note that this is not actually a `&str`
    let bytestring: &[u8; 21] = b"this is a byte string";

    // Byte arrays don't have the `Display` trait, so printing them is a bit limited
    println!("A byte string: {:?}", bytestring);

    // Byte strings can have byte escapes...
    let escaped = b"\x52\x75\x73\x74 as bytes";
    // ...but no unicode escapes
    // let escaped = b"\u{211D} is not allowed";
    println!("Some escaped bytes: {:?}", escaped);


    // Raw byte strings work just like raw strings
    let raw_bytestring = br"\u{211D} is not escaped here";
    println!("{:?}", raw_bytestring);

    // Converting a byte array to `str` can fail
    if let Ok(my_str) = str::from_utf8(raw_bytestring) {
        println!("And the same as text: '{}'", my_str);
    }

    let _quotes = br#"You can also use "fancier" formatting, \
                    like with normal raw strings"#;

    // Byte strings don't have to be UTF-8
    let shift_jis = b"\x82\xe6\x82\xa8\x82\xb1\x82\xbb"; // "ようこそ" in SHIFT-JIS

    // But then they can't always be converted to `str`
    match str::from_utf8(shift_jis) {
        Ok(my_str) => println!("Conversion successful: '{}'", my_str),
        Err(e) => println!("Conversion failed: {:?}", e),
    };
}

For conversions between character encodings check out the encoding crate.

A more detailed listing of the ways to write string literals and escape characters is given in the 'Tokens' chapter of the Rust Reference.


Option

Sometimes it's desirable to catch the failure of some parts of a program instead of calling panic!; this can be accomplished using the Option enum.

The Option<T> enum has two variants:

  • None, to indicate failure or lack of value, and
  • Some(value), a tuple struct that wraps a value with type T.
// An integer division that doesn't `panic!`
fn checked_division(dividend: i32, divisor: i32) -> Option<i32> {
    if divisor == 0 {
        // Failure is represented as the `None` variant
        None
    } else {
        // Result is wrapped in a `Some` variant
        Some(dividend / divisor)
    }
}

// This function handles a division that may not succeed
fn try_division(dividend: i32, divisor: i32) {
    // `Option` values can be pattern matched, just like other enums
    match checked_division(dividend, divisor) {
        None => println!("{} / {} failed!", dividend, divisor),
        Some(quotient) => {
            println!("{} / {} = {}", dividend, divisor, quotient)
        },
    }
}

fn main() {
    try_division(4, 2);
    try_division(1, 0);

    // Binding `None` to a variable needs to be type annotated
    let none: Option<i32> = None;
    let _equivalent_none = None::<i32>;

    let optional_float = Some(0f32);

    // Unwrapping a `Some` variant will extract the value wrapped.
    println!("{:?} unwraps to {:?}", optional_float, optional_float.unwrap());

    // Unwrapping a `None` variant will `panic!`
    println!("{:?} unwraps to {:?}", none, none.unwrap());
}

Result

We've seen that the Option enum can be used as a return value from functions that may fail, where None can be returned to indicate failure. However, sometimes it is important to express why an operation failed. To do this we have the Result enum.

The Result<T, E> enum has two variants:

  • Ok(value) which indicates that the operation succeeded, and wraps the value returned by the operation. (value has type T)
  • Err(why), which indicates that the operation failed, and wraps why, which (hopefully) explains the cause of the failure. (why has type E)
mod checked {
    // Mathematical "errors" we want to catch
    #[derive(Debug)]
    pub enum MathError {
        DivisionByZero,
        NonPositiveLogarithm,
        NegativeSquareRoot,
    }

    pub type MathResult = Result<f64, MathError>;

    pub fn div(x: f64, y: f64) -> MathResult {
        if y == 0.0 {
            // This operation would `fail`, instead let's return the reason of
            // the failure wrapped in `Err`
            Err(MathError::DivisionByZero)
        } else {
            // This operation is valid, return the result wrapped in `Ok`
            Ok(x / y)
        }
    }

    pub fn sqrt(x: f64) -> MathResult {
        if x < 0.0 {
            Err(MathError::NegativeSquareRoot)
        } else {
            Ok(x.sqrt())
        }
    }

    pub fn ln(x: f64) -> MathResult {
        if x <= 0.0 {
            Err(MathError::NonPositiveLogarithm)
        } else {
            Ok(x.ln())
        }
    }
}

// `op(x, y)` === `sqrt(ln(x / y))`
fn op(x: f64, y: f64) -> f64 {
    // This is a three level match pyramid!
    match checked::div(x, y) {
        Err(why) => panic!("{:?}", why),
        Ok(ratio) => match checked::ln(ratio) {
            Err(why) => panic!("{:?}", why),
            Ok(ln) => match checked::sqrt(ln) {
                Err(why) => panic!("{:?}", why),
                Ok(sqrt) => sqrt,
            },
        },
    }
}

fn main() {
    // Will this fail?
    println!("{}", op(1.0, 10.0));
}

?

Chaining results using match can get pretty untidy; luckily, the ? operator can be used to make things pretty again. ? is used at the end of an expression returning a Result, and is equivalent to a match expression, where the Err(err) branch expands to an early Err(From::from(err)), and the Ok(ok) branch expands to an ok expression.

mod checked {
    #[derive(Debug)]
    enum MathError {
        DivisionByZero,
        NonPositiveLogarithm,
        NegativeSquareRoot,
    }

    type MathResult = Result<f64, MathError>;

    fn div(x: f64, y: f64) -> MathResult {
        if y == 0.0 {
            Err(MathError::DivisionByZero)
        } else {
            Ok(x / y)
        }
    }

    fn sqrt(x: f64) -> MathResult {
        if x < 0.0 {
            Err(MathError::NegativeSquareRoot)
        } else {
            Ok(x.sqrt())
        }
    }

    fn ln(x: f64) -> MathResult {
        if x <= 0.0 {
            Err(MathError::NonPositiveLogarithm)
        } else {
            Ok(x.ln())
        }
    }

    // Intermediate function
    fn op_(x: f64, y: f64) -> MathResult {
        // if `div` "fails", then `DivisionByZero` will be `return`ed
        let ratio = div(x, y)?;

        // if `ln` "fails", then `NonPositiveLogarithm` will be `return`ed
        let ln = ln(ratio)?;

        sqrt(ln)
    }

    pub fn op(x: f64, y: f64) {
        match op_(x, y) {
            Err(why) => panic!("{}", match why {
                MathError::NonPositiveLogarithm
                    => "logarithm of non-positive number",
                MathError::DivisionByZero
                    => "division by zero",
                MathError::NegativeSquareRoot
                    => "square root of negative number",
            }),
            Ok(value) => println!("{}", value),
        }
    }
}

fn main() {
    checked::op(1.0, 10.0);
}

Be sure to check the documentation, as there are many methods to map/compose Result.


panic!

The panic! macro can be used to generate a panic and start unwinding its stack. While unwinding, the runtime will take care of freeing all the resources owned by the thread by calling the destructor of all its objects.

Since we are dealing with programs with only one thread, panic! will cause the program to report the panic message and exit.

// Re-implementation of integer division (/)
fn division(dividend: i32, divisor: i32) -> i32 {
    if divisor == 0 {
        // Division by zero triggers a panic
        panic!("division by zero");
    } else {
        dividend / divisor
    }
}

// The `main` task
fn main() {
    // Heap allocated integer
    let _x = Box::new(0i32);

    // This operation will trigger a task failure
    division(3, 0);

    println!("This point won't be reached!");

    // `_x` should get destroyed at this point
}

Let's check that panic! doesn't leak memory.

$ rustc panic.rs && valgrind ./panic
==4401== Memcheck, a memory error detector
==4401== Copyright (C) 2002-2013, and GNU GPL'd, by Julian Seward et al.
==4401== Using Valgrind-3.10.0.SVN and LibVEX; rerun with -h for copyright info
==4401== Command: ./panic
==4401== 
thread '<main>' panicked at 'division by zero', panic.rs:5
==4401== 
==4401== HEAP SUMMARY:
==4401==     in use at exit: 0 bytes in 0 blocks
==4401==   total heap usage: 18 allocs, 18 frees, 1,648 bytes allocated
==4401== 
==4401== All heap blocks were freed -- no leaks are possible
==4401== 
==4401== For counts of detected and suppressed errors, rerun with: -v
==4401== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)

HashMap

Where vectors store values by an integer index, HashMaps store values by key. HashMap keys can be booleans, integers, strings, or any other type that implements the Eq and Hash traits. More on this in the next section.

Like vectors, HashMaps are growable, but HashMaps can also shrink themselves when they have excess space. You can create a HashMap with a certain starting capacity using HashMap::with_capacity(uint), or use HashMap::new() to get a HashMap with a default initial capacity (recommended).

use std::collections::HashMap;

fn call(number: &str) -> &str {
    match number {
        "798-1364" => "We're sorry, the call cannot be completed as dialed. 
            Please hang up and try again.",
        "645-7689" => "Hello, this is Mr. Awesome's Pizza. My name is Fred.
            What can I get for you today?",
        _ => "Hi! Who is this again?"
    }
}

fn main() { 
    let mut contacts = HashMap::new();

    contacts.insert("Daniel", "798-1364");
    contacts.insert("Ashley", "645-7689");
    contacts.insert("Katie", "435-8291");
    contacts.insert("Robert", "956-1745");

    // Takes a reference and returns Option<&V>
    match contacts.get(&"Daniel") {
        Some(&number) => println!("Calling Daniel: {}", call(number)),
        _ => println!("Don't have Daniel's number."),
    }

    // `HashMap::insert()` returns `None`
    // if the inserted value is new, `Some(value)` otherwise
    contacts.insert("Daniel", "164-6743");

    match contacts.get(&"Ashley") {
        Some(&number) => println!("Calling Ashley: {}", call(number)),
        _ => println!("Don't have Ashley's number."),
    }

    contacts.remove(&"Ashley"); 

    // `HashMap::iter()` returns an iterator that yields 
    // (&'a key, &'a value) pairs in arbitrary order.
    for (contact, &number) in contacts.iter() {
        println!("Calling {}: {}", contact, call(number)); 
    }
}

For more information on how hashing and hash maps (sometimes called hash tables) work, have a look at Hash Table Wikipedia

Alternate/custom key types

Any type that implements the Eq and Hash traits can be a key in HashMap. This includes:

  • bool (though not very useful since there is only two possible keys)
  • int, uint, and all variations thereof
  • String and &str (protip: you can have a HashMap keyed by String and call .get() with an &str)

Note that f32 and f64 do not implement Hash, likely because floating-point precision errors would make using them as hashmap keys horribly error-prone.

All collection classes implement Eq and Hash if their contained type also respectively implements Eq and Hash. For example, Vec<T> will implement Hash if T implements Hash.

You can easily implement Eq and Hash for a custom type with just one line: #[derive(PartialEq, Eq, Hash)]

The compiler will do the rest. If you want more control over the details, you can implement Eq and/or Hash yourself. This guide will not cover the specifics of implementing Hash.

To play around with using a struct in HashMap, let's try making a very simple user logon system:

use std::collections::HashMap;

// Eq requires that you derive PartialEq on the type.
#[derive(PartialEq, Eq, Hash)]
struct Account<'a>{
    username: &'a str,
    password: &'a str,
}

struct AccountInfo<'a>{
    name: &'a str,
    email: &'a str,
}

type Accounts<'a> = HashMap<Account<'a>, AccountInfo<'a>>;

fn try_logon<'a>(accounts: &Accounts<'a>,
        username: &'a str, password: &'a str){
    println!("Username: {}", username);
    println!("Password: {}", password);
    println!("Attempting logon...");

    let logon = Account {
        username,
        password,
    };

    match accounts.get(&logon) {
        Some(account_info) => {
            println!("Successful logon!");
            println!("Name: {}", account_info.name);
            println!("Email: {}", account_info.email);
        },
        _ => println!("Login failed!"),
    }
}

fn main(){
    let mut accounts: Accounts = HashMap::new();

    let account = Account {
        username: "j.everyman",
        password: "password123",
    };

    let account_info = AccountInfo {
        name: "John Everyman",
        email: "j.everyman@email.com",
    };

    accounts.insert(account, account_info);

    try_logon(&accounts, "j.everyman", "psasword123");

    try_logon(&accounts, "j.everyman", "password123");
}

HashSet

Consider a HashSet as a HashMap where we just care about the keys ( HashSet<T> is, in actuality, just a wrapper around HashMap<T, ()>).

"What's the point of that?" you ask. "I could just store the keys in a Vec."

A HashSet's unique feature is that it is guaranteed to not have duplicate elements. That's the contract that any set collection fulfills. HashSet is just one implementation. (see also: BTreeSet)

If you insert a value that is already present in the HashSet, (i.e. the new value is equal to the existing and they both have the same hash), then the new value will replace the old.

This is great for when you never want more than one of something, or when you want to know if you've already got something.

But sets can do more than that.

Sets have 4 primary operations (all of the following calls return an iterator):

union: get all the unique elements in both sets.

difference: get all the elements that are in the first set but not the second.

intersection: get all the elements that are only in both sets.

symmetric_difference: get all the elements that are in one set or the other, but not both.

Try all of these in the following example:

use std::collections::HashSet;

fn main() {
    let mut a: HashSet<i32> = vec![1i32, 2, 3].into_iter().collect();
    let mut b: HashSet<i32> = vec![2i32, 3, 4].into_iter().collect();

    assert!(a.insert(4));
    assert!(a.contains(&4));

    // `HashSet::insert()` returns false if
    // there was a value already present.
    assert!(b.insert(4), "Value 4 is already in set B!");
    // FIXME ^ Comment out this line

    b.insert(5);

    // If a collection's element type implements `Debug`,
    // then the collection implements `Debug`.
    // It usually prints its elements in the format `[elem1, elem2, ...]`
    println!("A: {:?}", a);
    println!("B: {:?}", b);

    // Print [1, 2, 3, 4, 5] in arbitrary order
    println!("Union: {:?}", a.union(&b).collect::<Vec<&i32>>());

    // This should print [1]
    println!("Difference: {:?}", a.difference(&b).collect::<Vec<&i32>>());

    // Print [2, 3, 4] in arbitrary order.
    println!("Intersection: {:?}", a.intersection(&b).collect::<Vec<&i32>>());

    // Print [1, 5]
    println!("Symmetric Difference: {:?}",
             a.symmetric_difference(&b).collect::<Vec<&i32>>());
}

(Examples are adapted from the documentation.)


Rc

When multiple ownership is needed, Rc(Reference Counting) can be used. Rc keeps track of the number of the references which means the number of owners of the value wrapped inside an Rc.

Reference count of an Rc increases by 1 whenever an Rc is cloned, and decreases by 1 whenever one cloned Rc is dropped out of the scope. When an Rc's reference count becomes zero, which means there are no owners remained, both the Rc and the value are all dropped.

Cloning an Rc never performs a deep copy. Cloning creates just another pointer to the wrapped value, and increments the count.

use std::rc::Rc;

fn main() {
    let rc_examples = "Rc examples".to_string();
    {
        println!("--- rc_a is created ---");
        
        let rc_a: Rc<String> = Rc::new(rc_examples);
        println!("Reference Count of rc_a: {}", Rc::strong_count(&rc_a));
        
        {
            println!("--- rc_a is cloned to rc_b ---");
            
            let rc_b: Rc<String> = Rc::clone(&rc_a);
            println!("Reference Count of rc_b: {}", Rc::strong_count(&rc_b));
            println!("Reference Count of rc_a: {}", Rc::strong_count(&rc_a));
            
            // Two `Rc`s are equal if their inner values are equal
            println!("rc_a and rc_b are equal: {}", rc_a.eq(&rc_b));
            
            // We can use methods of a value directly
            println!("Length of the value inside rc_a: {}", rc_a.len());
            println!("Value of rc_b: {}", rc_b);
            
            println!("--- rc_b is dropped out of scope ---");
        }
        
        println!("Reference Count of rc_a: {}", Rc::strong_count(&rc_a));
        
        println!("--- rc_a is dropped out of scope ---");
    }
    
    // Error! `rc_examples` already moved into `rc_a`
    // And when `rc_a` is dropped, `rc_examples` is dropped together
    // println!("rc_examples: {}", rc_examples);
    // TODO ^ Try uncommenting this line
}

Arc

When shared ownership between threads is needed, Arc(Atomic Reference Counted) can be used. This struct, via the Clone implementation can create a reference pointer for the location of a value in the memory heap while increasing the reference counter. As it shares ownership between threads, when the last reference pointer to a value is out of scope, the variable is dropped.


fn main() {
use std::sync::Arc;
use std::thread;

// This variable declaration is where its value is specified.
let apple = Arc::new("the same apple");

for _ in 0..10 {
    // Here there is no value specification as it is a pointer to a reference
    // in the memory heap.
    let apple = Arc::clone(&apple);

    thread::spawn(move || {
        // As Arc was used, threads can be spawned using the value allocated
        // in the Arc variable pointer's location.
        println!("{:?}", apple);
    });
}
}

Original article source at https://doc.rust-lang.org

#rust #programming #developer