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Result

A Result monad implementation in .NET. Build more resilient applications by being explicit with what errors can be returned from your methods.

Getting Started

Installing

Install the NuGet package:

dotnet add package LSymds.Result

Creating results

You create results by calling Success or Erroneous on the Result<TSuccess, TError> type which builds a result that is in a successful or erroneous state respectively.

For example, to create a successful Result<string, MyErrorCode>:

return Result<string, MyErrorCode>.Successful("Success!");

and to create an erroneous Result<string, MyErrorCode>:

return Result<string, MyErrorCode>.Erroneous(MyErrorCode.Broken);

Creating results without a successful return type

To keep this library and any implementing code simple and easy to understand, I made the decision to implement one consistent interface (Result<TSuccess, TError>) regardless of whether TSuccess was a value of any substance or not.

As C# does not contain a Nothing type, this library provides one.

If you wish to return a result with a 'void' success type, you can do the following:

return Result<Nothing, MyErrorCode>.Successful(Nothing.Instance);

Utilities

Numerous utility methods hang off of the Result<TSuccess, TError> type.

  • Map - Returns a new result with the success type as the provided generic type, mapping the existing data value using the provided function and leaving the error value (if present) unchanged.
  • MapError - Performs similarly to Map, except it maps the error type and error value, leaving the data value (if present) unchanged.
  • Unwrap - UNSAFELY retrieves the value of Data, throwing an InvalidOperationException if the result is erroneous.
  • UnwrapOrElse - Retrieves the value of Data if the result is successful or the provided value if it isn't.