DiscriminatedUnion.CS 0.0.4-alpha

Discriminated Union

A library that provides functionality to define a Discriminated Union in C#.

Define some types

public class Success<T>
{
    public Success(T value)
    {
        Value = value;
    }

    public T Value { get; }
}

public class Error
{
    public Error(string message)
    {
        Message = message;
    }

    public string Message { get; }
}

Define union type

Union type must be an abstract, partial class marked with [GeneratedDiscriminatedUnion] attribute.

Every implementation of IDiscriminator<T> defines a discriminator inside the union type.

Where T is the type that constraints a discriminator.

[GeneratedDiscriminatedUnion]
public abstract partial class Result : IDiscriminator<Success<T>>, IDiscriminator<Error> { }

Use the union type

public class Program
{
    public static void Main(string[] args)
    {
        var result = GetRoot(-1);
        var outputMessage = result switch
        {
            Result<double>.Success s => s.Value.ToString(CultureInfo.InvariantCulture),
            Result<double>.Error e => e.Message,
        };

        Console.WriteLine(outputMessage);
    }

    public static Result<double> GetRoot(double value)
    {
        return value switch
        {
            < 0 => Result<double>.Error.Create("Value cannot be less than zero"),
            _ => Result<double>.Success.Create(Math.Sqrt(value))
        };
    }
}

Limitations

• Union one type multiple times not supported
• T.b.a