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https://github.com/vkhorikov/CSharpFunctionalExtensions

Functional extensions for C#
https://github.com/vkhorikov/CSharpFunctionalExtensions

csharp entity functional-programming maybe-monad result value-object

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Functional extensions for C#

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README 

        
# Functional Extensions for C#



[![Build Status](https://dev.azure.com/EnterpriseCraftsmanship/CSharpFunctionalExtensions/_apis/build/status/CSharpFunctionalExtensions?branchName=master)](https://dev.azure.com/EnterpriseCraftsmanship/CSharpFunctionalExtensions/_build/latest?definitionId=1&branchName=master)

[![NuGet downloads](https://img.shields.io/nuget/v/csharpfunctionalextensions.svg)](https://www.nuget.org/packages/CSharpFunctionalExtensions/)

[![GitHub license](https://img.shields.io/github/license/mashape/apistatus.svg)](https://github.com/vkhorikov/CSharpFunctionalExtensions/blob/master/LICENSE)



This library helps write code in more functional way.

To get to know more about the principles behind it, check out the [Applying Functional Principles in C# Pluralsight course](https://enterprisecraftsmanship.com/ps-func).



## Installation



Available on [NuGet](https://www.nuget.org/packages/CSharpFunctionalExtensions/)



```bash

dotnet add package CSharpFunctionalExtensions

```



or



```powershell

PM> Install-Package CSharpFunctionalExtensions

```



Also available as a strong named assembly (big thanks to [bothzoli](https://github.com/bothzoli) who made it possible!).



On [NuGet](https://www.nuget.org/packages/CSharpFunctionalExtensions.StrongName/)



```bash

dotnet add package CSharpFunctionalExtensions.StrongName

```



## Core Concepts



### Get rid of primitive obsession



```csharp

Result name = CustomerName.Create(model.Name);

Result email = Email.Create(model.PrimaryEmail);



Result result = Result.Combine(name, email);

if (result.IsFailure)

    return Error(result.Error);



var customer = new Customer(name.Value, email.Value);

```



## Make nulls explicit with the Maybe type



```csharp

Maybe customerOrNothing = _customerRepository.GetById(id);

if (customerOrNothing.HasNoValue)

    return Error("Customer with such Id is not found: " + id);

```



## Compose multiple operations in a single chain



```csharp

return _customerRepository.GetById(id)

    .ToResult("Customer with such Id is not found: " + id)

    .Ensure(customer => customer.CanBePromoted(), "The customer has the highest status possible")

    .Tap(customer => customer.Promote())

    .Tap(customer => _emailGateway.SendPromotionNotification(customer.PrimaryEmail, customer.Status))

    .Finally(result => result.IsSuccess ? Ok() : Error(result.Error));

```



## Wrap multiple operations in a TransactionScope



```csharp

return _customerRepository.GetById(id)

    .ToResult("Customer with such Id is not found: " + id)

    .Ensure(customer => customer.CanBePromoted(), "The customer has the highest status possible")

    .WithTransactionScope(customer => Result.Success(customer)

        .Tap(customer => customer.Promote())

        .Tap(customer => customer.ClearAppointments()))

    .Tap(customer => _emailGateway.SendPromotionNotification(customer.PrimaryEmail, customer.Status))

    .Finally(result => result.IsSuccess ? Ok() : Error(result.Error));

```



## API Examples



### Maybe



#### Explicit Construction



Use case: Creating a new Maybe containing a value



```csharp

Maybe apple = Maybe.From("apple");



// or



Maybe apple = Maybe.From("apple"); // type inference



// or



var apple = Maybe.From("apple");

```



#### None/No Value



Use case: Replacing `null` or the

[Null Object Pattern](https://enterprisecraftsmanship.com/2015/03/13/functional-c-non-nullable-reference-types/) for representing 'missing' data.



```csharp

int storeInventory = ...



Maybe fruit = storeInventory > 0

    ? Maybe.From("apple")

    : Maybe.None;



// or where the generic type is a reference type



Maybe fruit = null;



// or where the generic type is a value type



Maybe fruit = default;

```



#### Implicit Conversion



Use case: Easily creating a Maybe from a value



```csharp

// Constructing a Maybe

Maybe apple = "apple"; // implicit conversion



// Or as a method return value

Maybe GetFruit(string fruit)

{

    if (string.IsNullOrWhiteSpace(fruit))

    {

        return Maybe.None;

    }



    return fruit; // implicit conversion

}

```



#### Equality



Use case: Comparing Maybes or values without knowledge of the

inner value of the Maybes



```csharp

Maybe apple = "apple";

Maybe orange = "orange";

string alsoOrange = "orange";

Maybe noFruit = Maybe.None;



Console.WriteLine(apple == orange); // false

Console.WriteLine(apple != orange); // true

Console.WriteLine(orange == alsoOrange); // true

Console.WriteLine(alsoOrange == noFruit); // false

```



#### ToString



```csharp

Maybe apple = "apple";

Maybe noFruit = Maybe.None;



Console.WriteLine(apple.ToString()); // "apple"

Console.WriteLine(noFruit.ToString()); // "No value"

```



#### GetValueOrThrow



Use case: Procedurally accessing the inner value of the Maybe



**Note**: Calling this will throw a `InvalidOperationException` if there is no value



```csharp

Maybe apple = "apple";

Maybe noFruit = Maybe.None;



Console.WriteLine(apple.GetValueOrThrow()); // "apple";

Console.WriteLine(noFruit.GetValueOrThrow()); // throws InvalidOperationException !!

Console.WriteLine(noFruit.GetValueOrThrow(new CustomException())); // throws CustomException !!

```



#### HasValue and HasNoValue



Use case: Procedurally checking if the Maybe has a value,

usually before accessing the value directly



```csharp

void Response(string fruit)

{

    Console.WriteLine($"Yum, a {fruit} 😀");

}



Maybe apple = "apple";

Maybe noFruit = Maybe.None;



if (apple.HasValue)

{

    Response(apple.Value); // safe to access since we checked above

}



if (noFruit.HasNoValue)

{

    Response("We're all out of fruit 😢");

}

```



#### GetValueOrDefault



Use case: Safely accessing the inner value, without checking if there is one, by providing a fallback

if no value exists



```csharp

void Response(string fruit)

{

    Console.WriteLine($"It's a {fruit}");

}



Maybe apple = "apple";

Maybe unknownFruit = Maybe.None;



string appleValue = apple.GetValueOrDefault("banana");

string unknownFruitValue = unknownFruit.GetValueOrDefault("banana");



Response(appleValue); // It's a apple

Response(unknownFruitValue); // It's a banana

```



#### Where



Use case: Converting a Maybe with a value to a `Maybe.None` if a condition isn't met



**Note**: The predicate passed to `Where` (ex )



```csharp

bool IsMyFavorite(string fruit)

{

    return fruit == "papaya";

}



Maybe apple = "apple";



Maybe favoriteFruit = apple.Where(IsMyFavorite);



Console.WriteLine(favoriteFruit.ToString()); // "No value"

```



#### Map



Use case: Transforming the value in the Maybe, if there is one, without

needing to check if the value is there



**Note**: the delegate (ex `CreateMessage`) passed to `Maybe.Map()` is only executed if the Maybe has an inner value



```csharp

string CreateMessage(string fruit)

{

    return $"The fruit is a {fruit}";

}



Maybe apple = "apple";

Maybe noFruit = Maybe.None;



Console.WriteLine(apple.Map(CreateMessage).Unwrap("No fruit")); // "The fruit is a apple"

Console.WriteLine(noFruit.Map(CreateMessage).Unwrap("No fruit")); // "No fruit"

```



#### Select



**Alias**: `Maybe.Select()` is an alias of `Maybe.Map()`



#### Bind



Use case: Transforming from one Maybe into another Maybe

(like `Maybe.Map` but it transforms the Maybe instead of the inner value)



**Note**: the delegate (ex `MakeAppleSauce`) passed to `Maybe.Bind()` is only executed if the Maybe has an inner value



```csharp

Maybe MakeAppleSauce(Maybe fruit)

{

    if (fruit == "apple") // we can only make applesauce from apples 🍎

    {

        return "applesauce";

    }



    return Maybe.None;

}



Maybe apple = "apple";

Maybe banana = "banana";

Maybe noFruit = Maybe.None;



Console.WriteLine(apple.Bind(MakeAppleSauce).ToString()); // "applesauce"

Console.WriteLine(banana.Bind(MakeAppleSauce).ToString()); // "No value"

Console.WriteLine(noFruit.Bind(MakeAppleSauce).ToString()); // "No value"

```



#### SelectMany



**Alias**: `Maybe.SelectMany()` is an alias of `Maybe.Bind()`



#### Choose



Use case: Filter a collection of Maybes to only the ones that have a value,

and then return the value for each, or map that value to a new one



**Note**: the delegate passed to `Maybe.Choose()` is only executed on the Maybes of the collection with an inner value



```csharp

IEnumerable> unknownFruits = new[] { "apple", Maybe.None, "banana" };



IEnumerable knownFruits = unknownFruits.Choose();

IEnumerable fruitResponses = unknownFruits.Choose(fruit => $"Delicious {fruit}");



Console.WriteLine(string.Join(", ", knownFruits)) // "apple, banana"

Console.WriteLine(string.Join(", ", fruitResponses)) // "Delicious apple, Delicious banana"

```



#### Execute



Use case: Safely executing a `void` (or `Task`) returning operation on the Maybe inner value

without checking if there is one



**Note**: the `Action` (ex `PrintFruit`) passed to `Maybe.Execute()` is only executed if the Maybe has an inner value



```csharp

void PrintFruit(string fruit)

{

    Console.WriteLine($"This is a {fruit}");

}



Maybe apple = "apple";

Maybe noFruit = Maybe.None;



apple.Execute(PrintFruit); // "This is a apple"

noFruit.Execute(PrintFruit); // no output to the console

```



#### ExecuteNoValue



Use case: Executing a `void` (or `Task`) returning operation when the Maybe has no value



```csharp

void LogNoFruit(string fruit)

{

    Console.WriteLine($"There are no {fruit}");

}



Maybe apple = "apple";

Maybe banana = Maybe.None;



apple.ExecuteNoValue(() => LogNoFruit("apple")); // no output to console

banana.ExecuteNoValue(() => LogNoFruit("banana")); // "There are no banana"

```



#### Or



Use case: Supplying a fallback value Maybe or value in the case that the Maybe has no inner value



**Note**: The fallback `Func` (ex `() => "banana"`) will only be executed

if the Maybe has no inner value



```csharp

Maybe apple = "apple";

Maybe banana = "banana";

Maybe noFruit = Maybe.None;



Console.WriteLine(apple.Or(banana).ToString()); // "apple"

Console.WriteLine(noFruit.Or(() => banana)).ToString()); // "banana"

Console.WriteLine(noFruit.Or("banana").ToString()); // "banana"

Console.WriteLine(noFruit.Or(() => "banana").ToString()); // "banana"

```



#### Match



Use case: Defining two operations to perform on a Maybe.

One to be executed if there is an inner value, and the other to executed if there is not



```csharp

Maybe apple = "apple";

Maybe noFruit = Maybe.None;



// Void returning Match

apple.Match(

    fruit => Console.WriteLine($"It's a {fruit}"),

    () => Console.WriteLine("There's no fruit"));



// Mapping Match

string fruitMessage = noFruit.Match(

    fruit => $"It's a {fruit}",

    () => "There's no fruit"));



Console.WriteLine(fruitMessage); // "There's no fruit"

```



#### TryFirst and TryLast



Use case: Replacing `.FirstOrDefault()` and `.LastOrDefault()` so that you can return a

Maybe instead of a `null` or value type default value (like `0`, `false`) when working with collections



```csharp

IEnumerable fruits = new[] { "apple", "coconut", "banana" };



Maybe firstFruit = fruits.TryFirst();

Maybe probablyABanana = fruits.TryFirst(fruit => fruit.StartsWith("ba"));

Maybe aPeachOrAPear = fruits.TryFirst(fruit => fruit.StartsWith("p"));



Console.WriteLine(firstFruit.ToString()); // "apple"

Console.WriteLine(probablyABanana.ToString()); // "banana"

Console.WriteLine(aPeachOrAPear.ToString()); // "No value"



Maybe lastFruit = fruits.TryLast();

Maybe anAppleOrApricot = fruits.TryLast(fruit => fruit.StartsWith("a"));



Console.WriteLine(lastFruit.ToString()); // "banana"

Console.WriteLine(anAppleOrApricot.ToString()); // "apple"

```



#### TryFind



Use case: Safely getting a value out of a Dictionary



```csharp

Dictionary fruitInventory = new()

{

    { "apple", 10 },

    { "banana", 2 }

};



Maybe appleCount = fruitInventory.TryFind("apple");

Maybe kiwiCount = fruitInventory.TryFind("kiwi");



Console.WriteLine(appleCount.ToString()); // "10"

Console.WriteLine(kiwiCount.ToString()); // "No value"

```



#### ToResult



Use case: Representing the lack of an inner value in a Maybe as a failed operation



**Note**: See `Result` section below



```csharp

Maybe fruit = "banana";

Maybe noFruit = Maybe.None;



string errorMessage = "There was no fruit to give";



Result weGotAFruit = fruit.ToResult(errorMessage);

Result failedToGetAFruit = noFruit.ToResult(errorMessage);



Console.WriteLine(weGotAFruit.Value); // "banana"

Console.WriteLine(failedToGetAFruit.Error); // "There was no fruit to give"

```



#### ToUnitResult



Use case: Representing the lack of an inner value in a Maybe as a failed operation, if an Error is provided



Use case: Representing the presence of an inner value in a Maybe as a failed operation



**Note**: See `UnitResult` section below



```csharp

Maybe error = new Error();

Maybe noFruit = Maybe.None;



UnitResult weGotAnError = error.ToUnitResult();

UnitResult failedToGetAFruit = noFruit.ToUnitResult(new Error());



Console.WriteLine(weGotAnError.IsFailure); // true

Console.WriteLine(failedToGetAFruit.IsFailure); // true

```



### Result



#### Explicit Construction: Success and Failure



Use case: Creating a new Result in a Success or Failure state



```csharp

record FruitInventory(string Name, int Count);



Result appleInventory = Result.Success(new FruitInventory("apple", 4));

Result failedOperation = Result.Failure("Could not find inventory");

Result successInventoryUpdate = Result.Success();

```



To create a success result of a value you can also use the `Of` method which has overloads for `Func` and `Task`.



```csharp

Result something = Result.Of(_service.CreateSomething());

Result something = await Result.Of(_service.CreateSomethingAsync());

Result something = Result.Of(() => _service.CreateSomething());

Result something = await Result.Of(() => _service.CreateSomethingAsync());

```



#### Conditional Construction: SuccessIf and FailureIf



Use case: Creating successful or failed Results based on expressions or delegates instead of if/else statements or ternary expressions



```csharp

bool onTropicalIsland = true;



Result foundCoconut = Result.SuccessIf(onTropicalIsland, "These trees seem bare 🥥");

Result foundGrapes = Result.FailureIf(() => onTropicalIsland, "No grapes 🍇 here");



// or



bool isNewShipmentDay = true;



Result appleInventory = Result.SuccessIf(isNewShipmentDay, new FruitInventory("apple", 4), "No 🍎 today");

Result bananaInventory = Result.SuccessIf(() => isNewShipmentDay, new FruitInventory("banana", 2), "All out of 🍌");



// or



bool afterBreakfast = true;



Result orangeInventory = Result.FailureIf(afterBreakfast, new FruitInventory("orange", 10), "No 🍊 today");

Result grapefruitInventory = Result.FailureIf(() => afterBreakfast, new FruitInventory("grapefruit", 5), "No grapefruit 😢");

```



#### Implicit Conversion



Use case: Easily creating a successful result from a value



```csharp

Result appleInventory = new FruitInventory("apple", 4);

Result failedInventoryUpdate = "Could not update inventory";

```



#### ToString



Use case: Printing out the state of a Result and its inner value or error



```csharp

Result appleInventory = new FruitInventory("apple", 4);

Result bananaInventory = Result.Failure("Could not find any bananas");

Result failedInventoryUpdate = "Could not update inventory";

Result successfulInventoryUpdate = Result.Success();



Console.WriteLine(appleInventory.ToString()); // "Success(FruitInventory { Name = apple, Count = 4 })"

Console.WriteLine(bananaInventory.ToString()); // "Failure(Could not find any bananas)"

Console.WriteLine(failedInventoryUpdate.ToString()); // "Failure(Could not update inventory)"

Console.WriteLine(successfulInventoryUpdate.ToString()); // "Success"

```



#### Map



Use case: Transforming the inner value of a successful Result, without needing to check on

the success/failure state of the Result



**Note**: the delegate (ex `CreateMessage`) passed to `Result.Map()` is only executed if the Result was successful



```csharp

string CreateMessage(FruitInventory inventory)

{

    return $"There are {inventory.Count} {inventory.Name}(s)";

}



Result appleInventory = new FruitInventory("apple", 4);

Result bananaInventory = Result.Failure("Could not find any bananas");



Console.WriteLine(appleInventory.Map(CreateMessage).ToString()); // "Success(There are 4 apple(s))"

Console.WriteLine(bananaInventory.Map(CreateMessage).ToString()); // "Failure(Could not find any bananas)"

```



#### MapError



Use case: Transforming the inner error of a failed Result, without needing to check on

the success/failure state of the Result



**Note**: the delegate (ex `ErrorEnhancer`) passed to `Result.MapError()` is only executed if the Result failed



```csharp

string ErrorEnhancer(string errorMessage)

{

    return $"Failed operation: {errorMessage}";

}



Console.WriteLine(appleInventory.MapError(ErrorEnhancer).ToString()); // "Success(FruitInventory { Name = apple, Count = 4 })"

Console.WriteLine(bananaInventory.MapError(ErrorEnhancer).ToString()); // "Failed operation: Could not find any bananas"

```



## Testing



### CSharpFunctionalExtensions.FluentAssertions



A small set of extensions to make test assertions more fluent when using CSharpFunctionalExtensions! Check out the [repo for this library](https://github.com/NitroDevs/CSharpFunctionalExtensions.FluentAssertions) more information!



Includes custom assertions for

- Maybe

- Result

- Result

- Result

- UnitResult



#### Example



```csharp

var result = Result.Success(420);



result.Should().Succeed(); // passes

result.Should().SucceedWith(420); // passes

result.Should().SucceedWith(69); // throws

result.Should().Fail(); // throws

```



## Analyzers



### [CSharpFunctionalExtensions.Analyzers](https://github.com/AlmarAubel/CSharpFunctionalExtensions.Analyzers)

A Roslyn analyzer package that provides warnings and recommendations to prevent misuse of `Result` objects in `CSharpFunctionalExtensions`. Ensures more robust implementation when working with Result types.



Available on [NuGet](https://www.nuget.org/packages/CSharpFunctionalExtensions.Analyzers)

```bash

dotnet add package CSharpFunctionalExtensions.Analyzers

```



## Read or Watch more about these ideas



- [Functional C#: Primitive obsession](https://enterprisecraftsmanship.com/2015/03/07/functional-c-primitive-obsession/)

- [Functional C#: Non-nullable reference types](https://enterprisecraftsmanship.com/2015/03/13/functional-c-non-nullable-reference-types/)

- [Functional C#: Handling failures, input errors](https://enterprisecraftsmanship.com/2015/03/20/functional-c-handling-failures-input-errors/)

- [Applying Functional Principles in C# Pluralsight course](https://enterprisecraftsmanship.com/ps-func)



## Related Projects



- [Typescript Functional Extensions](https://github.com/seangwright/typescript-functional-extensions)

- [UniTask extensions for Unity](https://github.com/Razenpok/CSharpFunctionalExtensions.UniTask)



## Contributors



A big thanks to the project contributors!



- [Marcin Jahn](https://github.com/marcinjahn)

- [Jannes Kaspar-Müller](https://github.com/JKamue)

- [dbuckin1](https://github.com/dbuckin1)

- [bothzoli](https://github.com/bothzoli)

- [Pavel Zemlianikin](https://github.com/PNZeml)

- [Simon Lang](https://github.com/redx177)

- [Nils Vreman](https://github.com/NilsVreman)

- [Scheichsbeutel](https://github.com/Scheichsbeutel)

- [Alexey Malinin](https://github.com/TechnoBerry)

- [Robert Larkins](https://github.com/robertlarkins)

- [tinytownsoftware](https://github.com/tinytownsoftware)

- [piotr121993](https://github.com/piotr121993)

- [Dmitry Korotin](https://github.com/teheran)

- [michalsznajder](https://github.com/michalsznajder)

- [Xavier](https://github.com/xavierjohn)

- [Julien Aspirot](https://github.com/julienasp)

- [Kyle McMaster](https://github.com/KyleMcMaster)

- [Vinícius Beloni Cubas](https://github.com/vinibeloni)

- [rutkowskit](https://github.com/rutkowskit)

- [Giovanni Costagliola](https://github.com/MrBogomips)

- [Mark Wainwright](https://github.com/wainwrightmark)

- [ProphetLamb](https://github.com/ProphetLamb)

- [Paul Williams](https://github.com/Paul-Williams)

- [alexmurari](https://github.com/alexmurari)

- [ruud](https://github.com/ruudhe)

- [Tomasz Malinowski](https://github.com/Yaevh)

- [Staffan Wingren](https://github.com/staffanwingren)

- [Tim Schneider](https://github.com/DerStimmler)

- [Piotr Karasiński](https://github.com/Caleb9)

- [Marcel Roozekrans](https://github.com/MarcelRoozekrans)

- [guythetechie](https://github.com/guythetechie)

- [Logan Kahler](https://github.com/lqkahler)

- [Ali Khalili](https://github.com/AliKhalili)

- [Andrei Andreev](https://github.com/Razenpok)

- [YudApps](https://github.com/YudApps)

- [dataphysix](https://github.com/dataphysix)

- [Laszlo Lueck](https://github.com/LaszloLueck)

- [Sean G. Wright](https://github.com/seangwright)

- [Samuel Viesselman](https://github.com/SamuelViesselman)

- [Stian Kroknes](https://github.com/stiankroknes)

- [dataneo](https://github.com/dataneodev)

- [michaeldileo](https://github.com/michaeldileo)

- [Renato Ramos Nascimento](https://github.com/renato04)

- [Patrick Drechsler](https://github.com/draptik)

- [Vadim Mingazhev](https://github.com/mingazhev)

- [Darick Carpenter](https://github.com/darickc)

- [Stéphane Mitermite](https://github.com/kakone)

- [Markus Nißl](https://github.com/mnissl)

- [Adrian Frielinghaus](https://github.com/freever)

- [svroonland](https://github.com/svroonland)

- [JvSSD](https://github.com/JvSSD)

- [Vladimir Makaev](https://github.com/VladimirMakaev)

- [Ben Smith](https://github.com/benprime)

- [pedromtcosta](https://github.com/pedromtcosta)

- [Michał Bator](https://github.com/MikelThief)

- [mukmyash](https://github.com/mukmyash)

- [azm102](https://github.com/azm102)

- [ThomasDC](https://github.com/thomasdc)

- [bopazyn](https://github.com/bopazyn)

- [Joris Goovaerts](https://github.com/CommCody)

- [Ivan Deev](https://github.com/BillyFromAHill)

- [Damian Płaza](https://github.com/dpraimeyuu)

- [ergwun](https://github.com/ergwun)

- [Michael DiLeo](https://github.com/pilotMike)

- [Jean-Claude](https://github.com/jcsonder)

- [Matt Jenkins](https://github.com/space-alien)

- [Michael Altmann](https://github.com/altmann)

- [Steven Giesel](https://github.com/linkdotnet)

- [Anton Hryshchanka](https://github.com/ahryshchanka)

- [Mikhail Bashurov](https://github.com/saitonakamura)

- [kostekk88](https://github.com/kostekk88)

- [Carl Abrahams](https://github.com/CarlHA)

- [golavr](https://github.com/golavr)

- [Sviataslau Hankovich](https://github.com/hankovich)

- [Chad Gilbert](https://github.com/freakingawesome)

- [Robert Sęk](https://github.com/robosek)

- [Sergey Solomentsev](https://github.com/SergAtGitHub)

- [Malcolm J Harwood](https://github.com/mjharwood)

- [Dragan Stepanovic](https://github.com/dragan-stepanovic)

- [Ivan Novikov](https://github.com/jonny-novikov)

- [Denis Molokanov](https://github.com/dmolokanov)

- [Gerald Wiltse](https://github.com/solvingJ)

- [yakimovim](https://github.com/yakimovim)

- [Alex Erygin](https://github.com/alex-erygin)

- [Omar Aloraini](https://github.com/omaraloraini)