Branch	Status
main

• Installation
• Introduction
• Potential Corner Cases
• Use Cases
• Available API
  • Match and MatchAsync
  • Switch and SwitchAsync
  • IsGoodOutcome and IsBadOutcome
  • TryPickGoodOutcome(out TGoodOutcome? goodOutcome)
  • TryPickGoodOutcome(out TGoodOutcome? goodOutcome, out TBadOutcome? badOutcome)
  • TryPickBadOutcome(out TBadOutcome? badOutcome)
  • TryPickBadOutcome(out TGoodOutcome? goodOutcome, out TBadOutcome? badOutcome)
• Helpers
• Example Code Snippets

---

Installation

To install, run dotnet add package SharpOutcome or from Nuget

---

Introduction

SharpOutcome offers an implementation of the Result pattern featuring a straightforward API, enabling seamless code flow management without the need for exceptions.

There are two main types:

• Outcome<TGoodOutcome, TBadOutcome> which is a class.
• ValueOutcome<TGoodOutcome, TBadOutcome> which is a readonly record struct.

Both of them represent an outcome that can either be a good outcome of type TGoodOutcome or a bad outcome of type TBadOutcome. For TGoodOutcome and TBadOutcome, you can use any non-nullable type. Non-nullable means you can use FooBarbut not FooBar? or Nullable<FooBar>. This is intentional because nullability can be treated as a bad outcome. For convenience, helper interfaces along with their concrete implementations are provided.

Both types allow constructor creation or implicit conversion. For example, if a method has return type Task<ValueOutcome<IGoodOutcome, IBadOutcome>>, you can use the following patterns. Implicit return is preferred for cleaner code.

// use of constructor
return new ValueOutcome<IGoodOutcome, IBadOutcome>(new GoodOutcome(GoodOutcomeTag.Deleted));
// return based on implicit conversion
return new GoodOutcome(GoodOutcomeTag.Deleted);

---

Potential Corner Cases

• Since TGoodOutcome and TBadOutcome can take any non-nullable type, it is your responsibility to use them properly. No one will stop you from flipping the semantics. For example, you can use any non-nullable type for TBadOutcome that is meant for something good or success, but you shouldn't.

• TGoodOutcome and TBadOutcome must be of different type. For example, if a method has Outcome<string, string> as the return type, what's the benefit? In this case, you can just simply use string as return type.

• ValueOutcome is added for lowering the pressure on the garbage collector. Since C# enforces a parameterless constructor for struct type, no one will stop you doing the following:

ValueOutcome<string, int> MisuseOfValueOutcome()
{
    return new ValueOutcome<string, int>();
}

But you will get InvalidOperationException at runtime. If you want to enforce it in compile time, simply use Outcome type which has no parameterless public constructor.

The proper use of ValueOutcome should be the following:

ValueOutcome<string, int> ProperUseOfValueOutcome()
{
    if (RandomNumberGenerator.GetInt32(1, 10) == 5)
    {
        return "Ok";
    }

    return -1;
}

• Be careful when you use implicit conversion return feature from method. In the following code, you are returning int twice. If you are expecting BadOutcome as string, this will never happen because nothing is returned which has string as data type.

ValueOutcome<int, string> Gotcha()
{
    int number = RandomNumberGenerator.GetInt32(1, 10);

    if (number % 2 == 0)
    {
        return number;
    }

    return number;
}

---

Use Cases

• As method parameter value.
• Method return value.
• A complete REST API with CRUD functionality example is also given to showcase the usefulness of SharpOutcome. Source code is available here.
• Example code snippets.

---

Available API

Match and MatchAsync

The Match and MatchAsync methods execute a function on the good or bad outcome and return the result. If the outcome is bad, the function for the bad outcome is executed; otherwise, the function for the good outcome is executed.

return await result.MatchAsync<IActionResult>(
    entity => ResponseMakerAsync<Book, BookResponse>(HttpStatusCode.OK, entity),
    err => ResponseMaker(err)
);

---

Switch and SwitchAsync

The Switch and SwitchAsync methods execute an action on the good or bad outcome. If the outcome is bad, the action for the bad outcome is executed; otherwise, the action for the good outcome is executed. These methods do not return anything.

await result.SwitchAsync(
    entity => SendOkAsync(HttpStatusCode.OK, entity),
    err => SendBadRequestAsync(err)
);

---

IsGoodOutcome and IsBadOutcome

The IsGoodOutcome and IsBadOutcome get-only properties denote the status of the resolved outcome.

TryPickGoodOutcome(out TGoodOutcome? goodOutcome)

This method tries to extract the good outcome from the Outcome instance. If the instance represents a good outcome, it assigns the good outcome to the goodOutcome out parameter and returns true. If the instance represents a bad outcome, it assigns the default value to the goodOutcome out parameter and returns false.

var checkConfirmation = await CheckConfirmation(dto.Id);

if (checkConfirmation.TryPickGoodOutcome(out var goodOutcome))
{
    return new GoodOutcome(GoodOutcomeTag.Valid, goodOutcome.ToString());
}

TryPickGoodOutcome(out TGoodOutcome? goodOutcome, out TBadOutcome? badOutcome)

This overload of TryPickGoodOutcome tries to extract both the good and bad outcomes from the Outcome instance. If the instance represents a good outcome, it assigns the good outcome to the goodOutcome out parameter, the default value to the badOutcome out parameter, and returns true. If the instance represents a bad outcome, it assigns the default value to the goodOutcome out parameter, the bad outcome to the badOutcome out parameter, and returns false.

var result =  Demo.IdSender();

return result.TryPickGoodOutcome(out var good, out var bad)
    ? Results.Ok(good)
    : Results.BadRequest(bad);

TryPickBadOutcome(out TBadOutcome? badOutcome)

Functionality is same as TryPickGoodOutcomebut it tries to extract the bad outcome instead of the good outcome.

TryPickBadOutcome(out TGoodOutcome? goodOutcome, out TBadOutcome? badOutcome)

Functionality is same as TryPickGoodOutcomebut it tries to extract the bad outcome instead of the good outcome.

---

Helpers

For convenience, IGoodOutcome, IBadOutcome, IGoodOutcomeWithPayload, IBadOutcomeWithPayload interfaces are provided along with their concrete implementations GoodOutcome,BadOutcome, GoodOutcomeWithPayload, BadOutcomeWithPayload.

public interface IGoodOutcome
{
    GoodOutcomeTag Tag { get; }
    string? Reason { get; }
}


    public interface IGoodOutcome<out TOutcomeTag>
{
    TOutcomeTag Tag { get; }
    string? Reason { get; }
}

public interface IGoodOutcomeWithPayload<out TPayload>
{

    GoodOutcomeTag Tag { get; }
    TPayload Payload { get; }
    string? Reason { get; }
}


public interface IGoodOutcomeWithPayload<out TPayload, out TOutcomeTag>
{
    TOutcomeTag Tag { get; }
    TPayload Payload { get; }
    string? Reason { get; }
}

public interface IBadOutcome
{
    BadOutcomeTag Tag { get; }
    string? Reason { get; }
}


public interface IBadOutcome<out TOutcomeTag>
{
    TOutcomeTag Tag { get; }
    string? Reason { get; }
}

public interface IBadOutcomeWithPayload<out TPayload>
{
    BadOutcomeTag Tag { get; }
    TPayload Payload { get; }
    string? Reason { get; }
}

public interface IBadOutcomeWithPayload<out TPayload, out TOutcomeTag>
{
    TOutcomeTag Tag { get; }
    TPayload Payload { get; }
    string? Reason { get; }
}

---

Example Code Snippets

Here is an example with a service class method:

public async Task<Outcome<Book, IBadOutcome>> UpdateAsync(int id, BookRequest dto)
{
    try
    {
        Book? entityToUpdate = await _bookDbContext.Books.FindAsync(id);
        if (entityToUpdate is null) return new BadOutcome(BadOutcomeTag.NotFound);

        await dto.BuildAdapter().AdaptToAsync(entityToUpdate);
        _bookDbContext.Books.Attach(entityToUpdate);
        _bookDbContext.Entry(entityToUpdate).State = EntityState.Modified;
        await _bookDbContext.SaveChangesAsync();
        return entityToUpdate;
    }
    catch (Exception e)
    {
        Console.WriteLine(e);
        return new BadOutcome(BadOutcomeTag.Unexpected);
    }
}

The service class can be consumed in a controller class like the following way using the MatchAsync method:

[HttpPut("{id:int}")]
public async Task<IActionResult> PutBook(int id, BookRequest dto)
{
    if (!ModelState.IsValid) return ResponseMaker(HttpStatusCode.BadRequest);

    Outcome<Book, IBadOutcome> result = await _bookService.UpdateAsync(id, dto);

    return result.Match<IActionResult>(
        entity => ResponseMaker(HttpStatusCode.OK, entity),
        err => ResponseMaker(err)
    );
}

private IActionResult ResponseMaker(IBadOutcome error)
{
    var code = error.Tag switch
    {
        BadOutcomeTag.Failure => HttpStatusCode.InternalServerError,
        BadOutcomeTag.Unexpected => HttpStatusCode.InternalServerError,
        BadOutcomeTag.Validation => HttpStatusCode.BadRequest,
        BadOutcomeTag.Conflict => HttpStatusCode.Conflict,
        BadOutcomeTag.NotFound => HttpStatusCode.NotFound,
        BadOutcomeTag.Unauthorized => HttpStatusCode.Unauthorized,
        BadOutcomeTag.Forbidden => HttpStatusCode.Forbidden,
        _ => HttpStatusCode.InternalServerError,
    };

    return ResponseMaker(code, null, error.Reason);
}

private IActionResult ResponseMaker(HttpStatusCode code, object? data = null, string? message = null)
{
    if (code == HttpStatusCode.NoContent) return NoContent();

    var castedCode = (int)code;
    var isSuccess = castedCode is >= 200 and < 300;
    var res = new
    {
        Success = isSuccess,
        Message = message ?? ReasonPhrases.GetReasonPhrase(castedCode),
        Code = castedCode,
        Data = data
    };

    return StatusCode(castedCode, res);
}