DiscriminatedUnion.CS 0.0.2-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 and have to be marked with [GeneratedDiscriminatedUnion] attribute.

Every discriminator type must implement IDiscriminator<T> interface. Where T is the type that constraints a discriminator.

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

Use the union type

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

        Console.WriteLine(outputMessage);
    }

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

Limitations

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