union-struct

🚧 WORK IN PROGRESS 🚧

Union-struct is a zero-dependency library containing a source generator that generates memory-efficient union structs in C#. Union structs are value types that can store multiple types in the same memory location.

Motivation

This library is inspired by the Type Unions for C# proposal. At the time of writing, the prototype, implementation, and specification for this proposal have not been started.

It also takes inspiration from:

• OneOf
• Dunet
• Dusharp
• Intellenum

These are all great libraries. If this library doesn't suit your needs, I recommend checking them out.

I have not found a library that supports generating union structs with data that can be passed to ref parameters. This was the main motivation for creating this library.

This comes at the cost of memory-safety, as public fields need to be generated to allow this. Changing the data of a union struct can lead to memory corruption if not done correctly.

Examples

Basic Usage

using UnionStruct;

[Union]
internal partial struct VarIndex
{
	[UnionCase]
	public static partial VarIndex Unsigned8(byte index);

	[UnionCase]
	public static partial VarIndex Unsigned16(ushort index);

	[UnionCase]
	public static partial VarIndex Unsigned32(uint index);
}

Matching

Union structs can be matched using the Switch and Match methods.

VarIndex index = VarIndex.Unsigned8(123);
index.Switch(
	(u8) => Console.WriteLine($"Unsigned 8-bit index: {u8}"),
	(u16) => Console.WriteLine($"Unsigned 16-bit index: {u16}"),
	(u32) => Console.WriteLine($"Unsigned 32-bit index: {u32}"));

int size = index.Match(
	(u8) => sizeof(byte),
	(u16) => sizeof(ushort),
	(u32) => sizeof(uint));

Benchmarks

TODO

Development

Debugging the Source Generator

To debug the source generator, use the launchSettings.json file in the UnionStruct project to run the generator against the UnionStruct.Sample project.

You can also debug the generator tests using the UnionStruct.Tests project.

Snapshot Testing

To control which diff tool is used for snapshot testing, use the DiffEngine_ToolOrder environment variable.

In JetBrains Rider, this can be configured under Build, Execution, Deployment > Unit Testing > Test Runner > Environment variables.

You can also disable DiffEngine by setting the DiffEngine_Disable environment variable to true.

Personally, I use the Verify Support plugin for Rider.