MgResultPattern 1.0.0

MgResultPattern

A lightweight Result pattern library for .NET built on top of Dunet discriminated unions. It provides two generic union types — MgResult<T> and MgResults<T> — to represent the outcome of an operation without throwing exceptions.

Overview

FailureResponse carries a human-readable Message and an HTTP-style Code (defaults to 400).

Use MgResult<T> when an operation produces at most one error, and MgResults<T> when it can produce multiple errors (e.g. validation).

Installation

Add the project or package reference to your solution. The only dependency is Dunet (≥ 1.11.3) targeting .NET 10.

How to Use

Creating results

// Success
MgResult<int> ok = new MgResult<int>.Success(42);

// Failure with default code (400)
MgResult<int> fail = new MgResult<int>.Failure(new FailureResponse("Something went wrong"));

// Failure with explicit code
MgResult<int> serverError = new MgResult<int>.Failure(new FailureResponse("Unexpected error", 500));

Checking the outcome

if (result.IsSuccess())
{
    var value = result.GetSuccessValue();
}

if (result.IsFailure())
{
    var error = result.GetFailureValue(); // FailureResponse
    Console.WriteLine($"[{error.Code}] {error.Message}");
}

Pattern matching with Match

Match is the safest way to handle both cases exhaustively:

var message = result.Match(
    success => $"Got value: {success.Value}",
    failure => $"Error {failure.Value.Code}: {failure.Value.Message}"
);

Multiple failures with MgResults<T>

// Success
MgResults<string> ok = new MgResults<string>.Success("done");

// Multiple failures (e.g. validation)
var errors = new List<FailureResponse>
{
    new FailureResponse("Name is required", 422),
    new FailureResponse("Email is invalid", 422)
};
MgResults<string> fail = new MgResults<string>.Failure(errors);

if (fail.IsFailure())
{
    foreach (var error in fail.GetFailureValues())
        Console.WriteLine($"[{error.Code}] {error.Message}");
}

Returning results from a service

public MgResult<User> GetUser(int id)
{
    var user = _repository.Find(id);
    if (user is null)
        return new MgResult<User>.Failure(new FailureResponse("User not found", 404));

    return new MgResult<User>.Success(user);
}

Extension Methods

Both types expose the following helpers via C# extension methods:

Running Tests

dotnet test

Tests are written with xUnit and Shouldly and cover success/failure construction, IsSuccess/IsFailure guards, value retrieval, and Match exhaustiveness.