Ametrin.Optional

A modern, allocation-free library providing robust optional types for .NET. It offers a flexible and efficient way to handle nullable values, errors, and exceptions with a fluent, monadic API.

dotnet add package Ametrin.Optional

Features

• 🚀 Zero Allocation - Designed for high-performance scenarios
• 🧩 Monadic API - Fluent interface for transformations and error handling
• 🔄 Easy Integration - Seamless integration with existing C# code
• 🎯 Multiple Option Types - Different types for various use cases
• 💪 Async Support - First-class support for async operations

Core Types

Option<T>

Represents a value of type T or nothing (error state).

// Creating Options
Option<T> b = Option.Success(someT);    // explicit success creation (throws if someT is null)
Option<T> c = Option.Error<T>();        // explicit error creation
Option<T> a = Option.Of(someT);         // returns Option.Error<T>() if someT is null
Option<T> a = someT;                    // implicit conversion from T -> Option.Of(someT)
Option<T> d = default;                  // default results in an error state -> Option.Error<T>() 

Result<T> and Result<T, E>

Like Option<T> but with error information.
Result<T> stores an Exception as error
Result<T, E> stores a custom error type

Result<T> b = Result.Success(someT);            // explicit success creation (throws if someT is null)
Result<T> c = Result.Error<T>(new Exception()); // explicit error creation
Result<T> a = Result.Of(someT);                 // returns Result.Error<T>(new NullReferenceException()) if someT is null
Result<T> a = someT;                            // implicit conversion from T -> Result.Of(someT)
Result<T> a = new Exception();                  // implicit conversion from Exception -> Result.Error<T>(new Exception())
// same applies for Result<T, E> (with generic arguments)

ErrorState and ErrorState<E>

Represents a success state or an error value
ErrorState stores an Exception as error
ErrorState<E> stores a custom error type

ErrorState success = default;           // ErrorState.Success()
ErrorState error = new Exception();     // ErrorState.Success(new Exception())
// same applies for ErrorState<E> (with generic arguments)

Option

Represents a success state or error state. Holds no value.

Option success = true;          // Option.Success();
Option error = false;           // Option.Error();

Core API

// Common Operations
option.Map(value => value * 2);         // transform value if present
option.Require(x => x > 0);             // filter based on predicate
option.Reject(x => x > 0);              // inverse of Require
option.Or(defaultValue);                // provide default value
option.OrThrow();                       // throw if error
option.Match(                           // reduce to a value (equivalent to .Map(success).Or(error) but supports ref structs)
    success: value => value, 
    error: error => defaultValue
);
option.Consume(                         // handle success and error
    success: value => {}, 
    error: error => {}
);

Advanced Features

Tuple Operations

// Combine multiple options
(optionA, optionB).Map((a, b) => a + b);
(optionA, optionB).Consume(
    success: (a, b) => Console.WriteLine($"{a} + {b} = {a + b}"),
    error: () => Console.WriteLine("One of the values was missing")
);

Async Support

// Async operations with full option support
var text = await new FileInfo("file.txt")
    .RequireExists()
    .MapAsync(f => File.ReadAllTextAsync(f.FullName))
    .MapAsync(s => s.ToLower());

await text.ConsumeAsync(text => File.WriteAllTextAsync("output.txt", text));

RefOption<T>

Like Option<T> but can hold a ref struct as value

Edge Cases

For edge cases or high-performance scenarios where delegates cannot be static, use OptionsMarshall:

if(OptionsMarshall.IsSuccess(result))
{
    if(OptionsMarshall.TryGetValue(result, out var value))
    {
        // use value
    }
}

if(OptionsMarshall.TryGetError(result, out var error))
{
    // handle error
}

Testing

For testing code using Ametrin.Optional types, use the Ametrin.Optional.Testing.TUnit extensions:

await Assert.That(option).IsSuccess(expectedValue);
await Assert.That(option).IsError();

Contributing

Contributions are welcome! Feel free to:

• Create issues for bugs or feature requests
• Submit pull requests (discuss design first)
• Add extensions for more testing frameworks

Performance

The library is designed with performance in mind and has minimal to no overhead. Example benchmark for parsing a DateTime:

| Method            | Mean      | Error    | StdDev   | Allocated |
|------------------ |----------:|---------:|---------:|----------:|
| Default_Success   | 291.30 ns | 1.093 ns | 1.022 ns |         - |
| Option_Success    | 310.56 ns | 1.914 ns | 1.697 ns |         - |
| RefOption_Success | 300.98 ns | 1.454 ns | 1.360 ns |         - |
| Default_Error     |  72.12 ns | 0.289 ns | 0.226 ns |         - | // using TryParse
| Option_Error      |  67.75 ns | 0.324 ns | 0.287 ns |         - |
| RefOption_Error   |  72.75 ns | 0.145 ns | 0.136 ns |         - |