Zooper.Gorilla.Generators 1.3.0

Gorilla

<img src="icon.png" alt="drawing" width="256"/>

A .NET source generator for creating discriminated unions in C# with OneOf. Inspired by the flutter package freezed and the F# discriminated union pattern.

🚀 Overview

Gorilla helps you create type-safe, exhaustive discriminated unions in C#. It automatically generates matching methods, type checks, and conversions to make working with union types intuitive and safe. Gorilla uses OneOf under the hood to implement the discriminated union pattern but adds a layer of compile-time convenience and safety through source generation.

Gorilla supports:

• top-level flat unions
• unions nested inside classes, interfaces, and other containing types
• abstract hierarchical unions where nested sub-unions participate in outer Match(...) dispatch
• generated JSON converters for both flat and hierarchical unions

📦 Installation

# Install both packages
dotnet add package Zooper.Gorilla.Attributes
dotnet add package Zooper.Gorilla.Generators

🔧 Usage

1. Define your union type

Add the [DiscriminatedUnion] attribute to a partial type and declare one [Variant] factory per case:

using Zooper.Gorilla.Attributes;

[DiscriminatedUnion]
public partial class SignInError
{
	[Variant]
	public static partial SignInError ServiceUnavailable();

	[Variant]
	public static partial SignInError InvalidCredentials();

	[Variant]
	public static partial SignInError InternalError();
}

2. Use your union type

return SignInError.ServiceUnavailable();

🗃️ JSON Serialization

Gorilla can generate JSON converters automatically when your project references System.Text.Json or Newtonsoft.Json.

• System.Text.Json support emits a generated JsonConverter<T> and applies [System.Text.Json.Serialization.JsonConverter(...)]
• Newtonsoft.Json support emits a generated JsonConverter<T> and applies [Newtonsoft.Json.JsonConverterAttribute(...)]
• the discriminator field defaults to $type
• converter generation can be overridden per union with GenerateJsonConverter, GenerateNewtonsoftJsonConverter, and DiscriminatorFieldName

using System.Text.Json;

var value = CreateProfileDto.Person("John", "Doe");

var json = JsonSerializer.Serialize(value);
var roundTripped = JsonSerializer.Deserialize<CreateProfileDto>(json)!;

JSON support works for both flat unions and hierarchical unions.

🧩 Nested Unions

Nested unions can stay attached to the owning contract or payload type instead of being flattened into top-level declarations.

using Zooper.Gorilla.Attributes;

public partial interface IEntityCreatedContract
{
	public sealed record ContractVersion1(
		EntityId EntityId,
		EntityName Name,
		IEntityPayload Info,
		EntityOrder Order) : IEntityCreatedContract;

	public partial interface IEntityPayload
	{
		[DiscriminatedUnion]
		public sealed partial class V1 : IEntityPayload
		{
			[Variant]
			public static partial V1 Created();

			[Variant]
			public static partial V1 Standard(string category, bool isVisible);
		}
	}
}

That generated union can still be matched normally:

var payload = IEntityCreatedContract.IEntityPayload.V1.Standard("alpha", true);

var description = payload.Match(
	created => "created",
	standard => $"standard:{standard.Category}:{standard.IsVisible}");

See the full sample in Zooper.Gorilla.Sample/NestedContractSamples.cs.

🌲 Hierarchical Unions

Abstract unions can contain nested sub-unions that also flow through the outer union API.

using Zooper.Gorilla.Attributes;

[DiscriminatedUnion]
public abstract partial record ContractOutcome
{
	[Variant]
	public static partial ContractOutcome Success(string contractId);

	[DiscriminatedUnion]
	public abstract partial record Rejected : ContractOutcome
	{
		[Variant]
		public static partial Rejected Validation(string field);

		[DiscriminatedUnion]
		public abstract partial record Security : Rejected
		{
			[Variant]
			public static partial Security Unauthorized(string reason);
		}
	}
}

Each level gets its own Match(...), while nested values still participate in outer matching:

ContractOutcome outcome = ContractOutcome.Rejected.Security.Unauthorized("expired-session");

var description = outcome.Match(
	success => $"success:{success.ContractId}",
	rejected => rejected.Match(
		validation => $"validation:{validation.Field}",
		security => security.Match(
			unauthorized => $"unauthorized:{unauthorized.Reason}")));

See the sample in Zooper.Gorilla.Sample/ContractOutcome.cs.

🧪 Sample Project

The sample project includes:

• flat unions in Zooper.Gorilla.Sample/CreateProfileDto.cs, Zooper.Gorilla.Sample/SignInError.cs, and Zooper.Gorilla.Sample/SignUpError.cs
• nested contract-owned unions in Zooper.Gorilla.Sample/NestedContractSamples.cs
• hierarchical abstract unions in Zooper.Gorilla.Sample/ContractOutcome.cs

🤝 Contributing

Contributions are welcome! Please feel free to submit a Pull Request.

📄 License

This project is licensed under the MIT License - see the LICENSE file for details.

🙏 Acknowledgements

• OneOf - The foundation for this library
• F# Discriminated Unions - The inspiration for the pattern

Made with ❤️ by the Zooper team