A "lightweight" Maybe Monad for C#

The Maybe monad implemented here provides a way to handle optional values without resorting to explicit null checks, making your C# code cleaner, safer, and more readable. It aims to prevent the developer from accessing the value without checking it. This implementation supports async operations.

NuGet Package

The Atolye.Maybe package is available as a NuGet package. You can find it on the NuGet Gallery: Atolye.Maybe

Features

• Null Safety: Avoids null reference exceptions and encourages more functional programming patterns.
• Access Control: Prevents direct access to the base value without performing a control operation.
• Async Support: Seamlessly integrates with asynchronous programming models in .NET.
• Simplicity: Easy to use and understand, with a straightforward API.
• Flexibility: Provides methods to chain operations on the optional values, including checks and transformations, without unwrapping them.

Usage

Creating a Maybe instance

// Create a Maybe containing a value
Maybe<int> maybeInt = Maybe<int>.from(5);

// Create a Maybe containing an object
Maybe<Order> order = Maybe<Order>.from(orderData);

Working with Maybe

// Perform an operation if the value exists. In this example if orderData is not null, binds another operation.
Maybe<Order> order = Maybe<Order>.from(orderData)
                            .Bind(ord => AddOrderItems(ord, itemData));


// You can make pipelines.
Maybe<Order> order = Maybe<Order>.from(orderData)
                            .Bind(ord => AddOrderItems(ord, itemData))
                            .Bind(CalculateItemSums);


// You can set error messages if binded function returns null. It throws exception with specified message.
Maybe<Order> order = Maybe<Order>.from(orderData)
                            .Bind(ord => AddOrderItems(ord, itemData), "Throw this message if AddOrderItems returns null!")
                            .Bind(CalculateItemSums);


// You can use orElse to provide a default value or execute a callback function for null or empty values
Order order = Maybe<Order>.from(orderData)
    .OrElse(() => Maybe<Order>.from(new Order { Id = orderId, Status = "Pending" }))
    .ValueOrThrow("Failed to retrieve or create order");

Order order = Maybe<Order>.from(orderData)
    .OrElse(() => {
        Console.WriteLine($"Order {orderId} not found.");
    });


// Access unrwapped value if it is not null, otherwise throws exception with specified message.
Order order = Maybe<Order>.from(orderData)
                            .Bind(ord => AddOrderItems(ord, itemData))
                            .Bind(CalculateItemSums)
                            .ValueOrThrow("Can not create order!");

Value Checking

// Perform checks with data based on a predicate. If check fails it returns an empty Maybe.
Maybe<Order> order = Maybe<Order>.from(orderData)
                            .Check(ord => ord.ItemCount > 0);

// If you specify error message, it will throw exception with the message.
Maybe<Order> order = Maybe<Order>.from(orderData)
                            .Check(ord => ord.ItemCount > 0, "Order must have at least 1 item!");

// You can create a validation pipeline.
Maybe<Order> order = Maybe<Order>.from(orderData)
                            .Check(ord => ord.ItemCount > 0, "Order must have at least 1 item!")
                            .Check(ord => !string.IsNullOrEmpty(ord.CustomerName), "Customer name must be specified!");

// You check null and throw exception before binding functions.
Order order = Maybe<Order>.from(orderData)
                        .CheckNull("Invalid order data!")
                        .Bind(CreateOrderItems)
                        .ValueOrThrow("Can not create order!");

// You validate input and throw exception before binding functions.
Order order = Maybe<Order>.from(orderData)
                        .Check(ValidateOrderData, "Invalid order data!")
                        .Bind(CreateOrderItems)
                        .ValueOrThrow("Can not create order!");

Using the With Method

The With method provided by the Maybe monad allows for the modification of the underlying value while preserving the optional nature of the Maybe type.

Order order = Maybe<Order>.from(orderData)
                        .With(
                            ord => ord.CustomerName = "Modified or newly added Customer Name",
                            ord => ord.Location = "Modified or newly added Location"
                        )
                        .ValueOrThrow("Can not get order!");

Async Support

The library extends its functionality to asynchronous operations, allowing the Maybe type to be used with async/await patterns seamlessly.

// You can use async functions for check and bind.
Order order = await Maybe<Order>.from(orderData)
                        .CheckAsync(async ord => await ValidateFromRemote(ord), "Invalid order data!")
                        .BindAsync(async ord => await CreateOrderFromRemoteService(ord))
                        .ValueOrThrow("Can not create order!");

License

Copyright (c) Atölye Dijital 2022

This project is open-sourced under the MIT license. See the LICENSE file for details.