Toarnbeike.Optional.TestExtensions 1.0.1

Toarnbeike.Optional

Toarnbeike.Optional is a lightweight, expressive C# implementation of the Option (Maybe) monad.

It improves code clarity and safety by making the absence of a value explicit, replacing null checks and exceptions with a functional approach.

Developed by Toarnbeike for personal and professional use in domain-driven and functional designs.

Features

• Fluent API for working with optional values
• Implicit conversion from values and Option.None
• Extension methods inspired by F#, Rust and Haskell
• Full support for Task<Option<T>> async scenarios
• Rich LINQ-style extensions for IEnumerable<Option<T>>
• Assertion syntax similar to Shouldly for test projects
• [Planned] Linq integration (query syntax)

Packages

Package	Description	NuGet
Toarnbeike.Optional	Core option type, extension methods and collections
Toarnbeike.Optional.TestExtensions	Assertion helpers for Option<T> in tests

Inspiration

This project draws ideas from:

• Zoran Horvat (youtube)
• nlkl.Optional (github)
• DotnetFunctional.Maybe (github)

Getting Started

dotnet add package Toarnbeike.Optional

Then import the namespace in your code:

using Toarnbeike.Optional;			// Base namespace for Option<T>
using Toarnbeike.Optional.Collections;		// For collection extensions
using Toarnbeike.Optional.Extensions;		// For functional extensions on Option<T>

Basic Usage

An option can represent either a value (Some) or no value (None):

var option1 = Option<int>.Some(1);
var option2 = Option.Some(1);        // Type inferred
var option3 = Option<int>.None();

Option<int> option4 = 1;             // Implicit conversion
Option<int> option5 = Option.None;

Extracting the value:

if (option1.TryGetValue(out var value))
{
    Console.WriteLine(value); // Outputs: 1
}

Extension Methods

The Toarnbeike.Optional.Extensions namespace includes rich extensions for Option<T>:

Available Extensions

Collections

The Toarnbeike.Optional.Collections namespace adds functional utilities to collections of Option<T>:

using Toarnbeike.Optional.Collections;

var options = new List<Option<int>>([1, Option.None, 3]);

var values = options.Values();					// [1, 3]
var filtered = options.WhereValues(i => i > 1);			// [3]
var doubled = options.SelectValues(i = > i * 2);		// [2,6] 
var evenCount = options.CountValues(i => i % 2 == 0);		// Option.None
var first = options.FirstOrNone(i => i > 2);			// Option.Some(3)
var last = options.LastOrNone(i => i > 0);			// Opiton.Some(3)

Also works on IEnumerable<T>:

using Toarnbeike.Optional.Collections;
var numbers = new List<int> { 1, 2, 3 };

var first = options.FirstOrNone(i => i > 4);			// Option.None
var last = options.LastOrNone(i => i > 0);			// 3 (as regular int)

Try Helpers

Use Option.Try(...) to wrap exception-throwing code like parsing, config loading, etc.
Returns Option.None when an exception occurs (with optional filtering and logging).

var result = Option.Try(() => int.Parse("123")); // Option.Some(123)
var fallback = Option.Try(() => int.Parse("abc")); // Option.None

// With optional filtering and logging
var parsed = Option.Try(
    () => int.Parse("abc"),
    ex => ex is FormatException,
    ex => logger.Warn(ex, "Invalid number")
);

Optional.TestExtensions

Toarnbeike.Optional.TestExtensions provides simple assertion methods to improve test readability for Option<T> instances.

Example

Option<string> option = Option.Some("value");
option.ShouldBeSomeWithValue("value");

Available Assertions

Installation

dotnet add package Toarnbeike.Optional.TestExtensions

Why Option?

Because nulls are dangerous and exceptions are control-flow. Using Option<T>:

• Makes absence explicit
• Forces handling at compile time
• Composes beautifully in pipelines

Make illegal states unrepresentable.