W4k.Either /ˈaɪ.ðə^r/

Why?

There are several ways to handle the results of operations in C#. For instance, you could:

• Throw an exception: However, this can be costly and isn't always appropriate. Exceptions can be thought of as goto commands within the entire call stack.
• Return a tuple: While this method is feasible, it is not very descriptive and can clutter your code.
• Write a unique result type for every operation: This approach requires significant effort, and we know developers prefer efficiency.

A more practical solution is to use this project.

What?

This project is source for two packages:

• W4k.Either: Predefined types that can be used to represent discriminated union.
• W4k.Either.CodeGeneration: Provides source generator that can be used to generate your own types with custom logic/rules.

Please follow links above to get more information about each package.

Example of Either<TLeft, TRight>:

Either<User, FetchError> GetUser(UserIdentifier userId)
{
    try
    {
        // ...
        return new User(...);
    }
    catch (Exception ex)
    {
        return new FetchError(ex);
    }
}

var result = GetUser(userId);
var message = result.Match(
    user => $"User {user.Name} fetched",
    error => $"Error {error.Message} occured"
);

Types provided by library

Type	Description
Either<TLeft, TRight>	Discriminated union of two or more types
Maybe<TValue>	Optional value representation
Result<TError>	Result representation without a value
Result<TValue, TError>	Result representation with a value
OptionalResult<TValue, TError>	Optional result with a value (similar to Result<Maybe, TError>)

More details about each type can be found here.

Generating own types

You can generate your own types with custom logic/rules:

[Either]
public readonly partial struct Gelf<TCamille, TCat, TCrichton>
{
}

Please follow this link to get more information.

Alternative/similar packages

Listed alphabetically

• Ardalis.Result: A simple implementation of Result for C#
• CSharpFunctionalExtensions: Functional extensions for C#
• Danom: Danom is a C# library that provides (monadic) structures...
• dunet: Simple source generator for discriminated unions in C#
• ErrorOr: A simple, fluent discriminated union of an error or a result
• FluentResults: A lightweight .NET library to handle errors and failures in a fluent way
• FxKit: A library for C# to enable functional, railway-oriented programming using common abstract data types
• LanguageExt: Provides functional-programming "base class" library
• Nut.Result: Provides an object in .NET that represents the result of a simple process
• OneOf: Discriminated unions for C#
• Optional: A robust option/maybe type for C#
• Result.Net: A simple wrapper over an operation execution results to indicate success or failure
• SimpleResults: A simple library to implement the Result pattern for returning from services

Additional resources

Technical notes describing possible states of monad regarding to C# type system, here.

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