Dunet is a simple source generator for discriminated unions in C#.
- NuGet:
dotnet add package dunet
// 1. Import the namespace.
using Dunet;
// 2. Add the `Union` attribute to a partial record.
[Union]
partial record Shape
{
// 3. Define the union members as inner partial records.
partial record Circle(double Radius);
partial record Rectangle(double Length, double Width);
partial record Triangle(double Base, double Height);
}
// 4. Use the union members.
var shape = new Shape.Rectangle(3, 4);
var area = shape.Match(
circle => 3.14 * circle.Radius * circle.Radius,
rectangle => rectangle.Length * rectangle.Width,
triangle => triangle.Base * triangle.Height / 2
);
Console.WriteLine(area); // "12"Use generics for more advanced union types. For example, an option monad:
// 1. Import the namespace.
using Dunet;
// 2. Add the `Union` attribute to a partial record.
// 3. Add one or more type arguments to the union record.
[Union]
partial record Option<T>
{
partial record Some(T Value);
partial record None();
}
// 4. Use the union members.
static Option<int> ParseInt(string? value) =>
int.TryParse(value, out var number)
? Option<int>.Some(number)
: Option<int>.None();
static string GetOutput(Option<int> number) =>
number.Match(
some => some.Value.ToString(),
none => "Invalid input!"
);
var input = ParseInt(Console.ReadLine()); // User inputs "not a number".
Console.WriteLine(GetOutput(input)); // "Invalid input!"
input = ParseInt(Console.ReadLine()); // User inputs "12345".
Console.WriteLine(GetOutput(input)); // "12345".