N.SourceGenerators.UnionTypes 0.4.0

N.SourceGenerators.UnionTypes

Discriminated union type source generator

Motivation

C# doesn't support discriminated unions yet. This source generator helps automate writing union types.

Using

Add package reference to N.SourceGenerators.UnionTypes

dotnet add package N.SourceGenerators.UnionTypes

Create a partial class that will be used as a union type

public partial class FooResult
{
}

Add types you want to use in a discriminated union

public record Success(int Value);
public record ValidationError(string Message);
public record NotFoundError;

public partial class FooResult
{
}

Add N.SourceGenerators.UnionTypes.UnionTypeAttribute to a union type.

using N.SourceGenerators.UnionTypes;

public record Success(int Value);
public record ValidationError(string Message);
public record NotFoundError;

[UnionType(typeof(Success))]
[UnionType(typeof(ValidationError))]
[UnionType(typeof(NotFoundError))]
public partial class FooResult
{
}

Examples

All examples can be found in examples project

Implicit conversion

public FooResult ImplicitReturn()
{
    // you can return any union type variation without creating FooResult
    return new NotFoundError();
}

Explicit conversion

public ValidationError ExplicitCast(FooResult result)
{
    return (ValidationError)result;
}

Match and MatchAsync methods force you to handle all possible variations

public IActionResult MatchMethod(FooResult result)
{
    return result.Match<IActionResult>(
        success => new OkResult(),
        validationError => new BadRequestResult(),
        notFoundError => new NotFoundResult()
    );
}

public async Task<IActionResult> MatchAsyncMethod(FooResult result, CancellationToken cancellationToken)
{
    return await result.MatchAsync<IActionResult>(
        static async (success, ct) =>
        {
            await SomeWork(ct);
            return new OkResult();
        }, static async (validationError, ct) =>
        {
            await SomeWork(ct);
            return new BadRequestResult();
        }, static async (notFoundError, ct) =>
        {
            await SomeWork(ct);
            return new NotFoundResult();
        }, cancellationToken);

    static Task SomeWork(CancellationToken ct)
    {
        return Task.Delay(100, ct);
    }
}