Aigamo.MatchGenerator 0.0.0-preview013

MatchGenerator

Bring exhaustive pattern matching to C# enums and unions with zero boilerplate.

MatchGenerator is a Roslyn source generator that creates Match extension methods for your enums and discriminated-union-like types, enabling concise, expressive, and compile-time safe branching.

Features

• Generate Match extension methods for enums and unions
• Exhaustive by design (no missing cases)
• Attribute-driven (opt-in per type)
• Supports generics (Match<U>)
• Respects effective accessibility
• Zero runtime cost (pure source generation)

Getting Started

1. Install the package

dotnet add package Aigamo.MatchGenerator

2. Annotate your type

Enum example

using Aigamo.MatchGenerator;

[GenerateMatch]
public enum Gender
{
	Male = 1,
	Female,
}

Union example

using Aigamo.MatchGenerator;

[GenerateMatch]
abstract record MaritalStatus;

sealed record Single : MaritalStatus;
sealed record Married : MaritalStatus;
sealed record Divorced : MaritalStatus;
sealed record Widowed : MaritalStatus;

3. Use Match

Enum

var message = gender.Match(
	onMale: () => "male",
	onFemale: () => "female"
);

Union

var message = maritalStatus.Match(
	onSingle: x => "single",
	onMarried: x => "married",
	onDivorced: x => "divorced",
	onWidowed: x => "widowed"
);

Why use MatchGenerator?

Without MatchGenerator

Enum

var message = gender switch
{
	Gender.Male => "male",
	Gender.Female => "female",
	_ => throw new UnreachableException(),
};

Union

var message = maritalStatus switch
{
	Single x => "single",
	Married x => "married",
	Divorced x => "divorced",
	Widowed x => "widowed",
	_ => throw new UnreachableException(),
};

With MatchGenerator

var message = gender.Match(
	onMale: () => "male",
	onFemale: () => "female"
);

• More concise
• More readable
• No default case required
• Compile-time safety

Exhaustiveness Guarantee

All cases must be handled.

If a new enum value or union type is added:

public enum Gender
{
	Male = 1,
	Female,
	Other,
}

or

sealed record Separated : MaritalStatus;

Existing Match calls will fail to compile until updated. This ensures no cases are missed.

Generated Code (Example)

Enum

internal static class GenderMatchExtensions
{
	public static U Match<U>(
		this Gender value,
		Func<U> onFemale,
		Func<U> onMale
	)
	{
		return value switch
		{
			Gender.Female => onFemale(),
			Gender.Male => onMale(),
			_ => throw new UnreachableException(),
		};
	}
}

Union

internal static class MaritalStatusMatchExtensions
{
	public static U Match<U>(
		this MaritalStatus value,
		Func<Divorced, U> onDivorced,
		Func<Married, U> onMarried,
		Func<Single, U> onSingle,
		Func<Widowed, U> onWidowed
	)
	{
		return value switch
		{
			Divorced x => onDivorced(x),
			Married x => onMarried(x),
			Single x => onSingle(x),
			Widowed x => onWidowed(x),
			_ => throw new UnreachableException(),
		};
	}
}

References

• Introducing C# Source Generators - .NET Blog
• roslyn/docs/features/source-generators.cookbook.md at main · dotnet/roslyn
• roslyn/docs/features/incremental-generators.cookbook.md at main · dotnet/roslyn
• Domain Modeling Made Functional: Tackle Software Complexity with Domain-Driven Design and F# by Scott Wlaschin
• It Seems the C# Team Is Finally Considering Supporting Discriminated Unions - DEV Community
• salvois/DiscriminatedOnions: A stinky but tasty hack to emulate F#-like discriminated unions in C#