Matches.SourceGeneration 2.1.0

Matches.SourceGeneration

A C# source generator that automatically creates discriminated union types and Match methods from enums.

Usage

The library provides two attributes:

• [DiscriminatedUnion] – marks an enum as a discriminated union.
• [DiscriminatedUnionCase] – assigns a type to an enum case.

When the project is built, interfaces, records, and helper methods are generated automatically.

Example: Simple types

Mark the ContactKind enum as a discriminated union and assign types to its cases:

[DiscriminatedUnion]
public enum ContactKind
{
    [DiscriminatedUnionCase(typeof(Email))]
    Email,

    [DiscriminatedUnionCase(typeof(Phone))]
    Phone,

    [DiscriminatedUnionCase(typeof(WebHook))]
    WebHook
}

Generated on build:

• IContact interface
• EmailContact, PhoneContact, and WebHookContact records
• Contact static class with factory and Match methods

Usage example:

const string message = "hmm";

IContact[] contacts =
[
    Contact.GetEmailContact(new Email("aaa@bbb.com")),
    Contact.GetPhoneContact(new Phone(380, 1234567)),
    Contact.GetWebHookContact(new WebHook(new Uri("https://okak.kot")))
];

foreach (var contact in contacts)
{
    var res = SendMessage(contact, message);
    Console.WriteLine(res);
}

static string SendMessage(IContact contact, string text) =>
    Contact.Match
    (
        contact,
        email   => $"'{text}' sent to {email.Address} email address",
        phone   => $"'{text}' sent to +{phone.Code}{phone.Number} phone number",
        webHook => $"'{text}' sent to {webHook.Uri} webhook URI"
    );

Output:

'hmm' sent to aaa@bbb.com email address
'hmm' sent to +3801234567 phone number
'hmm' sent to https://okak.kot/ webhook URI

Example: Generic types

Bound generic types are supported the same way as simple ones.

To generate types with generic parameters, specify the unbound generic type and provide arguments in order:

• a concrete type → binds the parameter
• null or GenericPlaceholder → keeps it as a generic parameter in the generated type

[DiscriminatedUnion]
public enum WebRequestResultKind
{
    [DiscriminatedUnionCase(typeof(RequestData<,,>), typeof(string), null, typeof(GenericPlaceholder))]
    Success,

    [DiscriminatedUnionCase(typeof(List<>), (Type?)null)]
    Warnings,

    [DiscriminatedUnionCase(typeof(List<string>))]
    Errors
}

public record RequestData<TKey, TData, TItem>(TData Data) 
    where TData : IDictionary<TKey, TItem> 
    where TItem : struct;

public record WarningInfo(int Code, string Message);

More examples

Check out the Matches.Tests project for additional usage patterns.

License

This project is dedicated to the public domain under the Unlicense.
See the LICENSE file for details.