C#•13mo ago

✅ Is it possible to use union type in C#?

I'm not sure that it's called exactly Union Type Let me introduce the issue I have this class which represent generator:

public class UISchemaGenerator
{
    private readonly ConcurrentDictionary<(CustomFieldSet, CultureInfo), UISchemaSpecification> _cache =
        new();

    public UISchemaSpecification Generate(
        CustomFieldSet fieldSet,
        MandatorySecurityScope scope,
        CultureInfo culture = default)
    {
        culture ??= CultureInfo.CurrentCulture;

        return _cache.GetOrAdd(
            key: (fieldSet, culture),
            valueFactory: _ => InternalGenerator(fieldSet, scope, culture));
    }

    private UISchemaSpecification InternalGenerator(
        CustomFieldSet fieldSet,
        MandatorySecurityScope scope,
        CultureInfo culture)
    {
        var schemaBuilder = new UISchemaBuilder();

        foreach (var group in fieldSet.Groups)
        {
            schemaBuilder
                .StartGroup(group.Title)
                    .AddFields(scope, group.Fields)
                .EndGroup();
        }

        return schemaBuilder.Build();
    }

    private UISchemaSpecification InternalGenerator(
        CustomField.CustomField fieldSet,
        MandatorySecurityScope scope,
        CultureInfo culture)
    {
        var schemaBuilder = new UISchemaBuilder()
            .AddField(fieldSet)
            .Build();

        return schemaBuilder;
    }
}

public class UISchemaGenerator
{
    private readonly ConcurrentDictionary<(CustomFieldSet, CultureInfo), UISchemaSpecification> _cache =
        new();

    public UISchemaSpecification Generate(
        CustomFieldSet fieldSet,
        MandatorySecurityScope scope,
        CultureInfo culture = default)
    {
        culture ??= CultureInfo.CurrentCulture;

        return _cache.GetOrAdd(
            key: (fieldSet, culture),
            valueFactory: _ => InternalGenerator(fieldSet, scope, culture));
    }

    private UISchemaSpecification InternalGenerator(
        CustomFieldSet fieldSet,
        MandatorySecurityScope scope,
        CultureInfo culture)
    {
        var schemaBuilder = new UISchemaBuilder();

        foreach (var group in fieldSet.Groups)
        {
            schemaBuilder
                .StartGroup(group.Title)
                    .AddFields(scope, group.Fields)
                .EndGroup();
        }

        return schemaBuilder.Build();
    }

    private UISchemaSpecification InternalGenerator(
        CustomField.CustomField fieldSet,
        MandatorySecurityScope scope,
        CultureInfo culture)
    {
        var schemaBuilder = new UISchemaBuilder()
            .AddField(fieldSet)
            .Build();

        return schemaBuilder;
    }
}

I want somehow add following logic:

public UISchemaSpecification Generate(
   Union<CustomField, CustomFieldSet> fieldSet,
   MandatorySecurityScope scope,
   CultureInfo culture = default)
{
    // if someone passed CustomField then call InternalGenerator for CustomField
    // if someone passed CustomFieldSetthen call InternalGenerator for CustomFieldSet
}

public UISchemaSpecification Generate(
   Union<CustomField, CustomFieldSet> fieldSet,
   MandatorySecurityScope scope,
   CultureInfo culture = default)
{
    // if someone passed CustomField then call InternalGenerator for CustomField
    // if someone passed CustomFieldSetthen call InternalGenerator for CustomFieldSet
}

I don't want to override method because it will be too much code in one class dictionary x2, Generate x2, InternalGenerator x2

9 Replies

PresidentNotSure•13mo ago

https://learn.microsoft.com/en-us/dotnet/api/system.linq.enumerable.union?view=net-7.0

Enumerable.Union Method (System.Linq)

Produces the set union of two sequences.

SWEETPONY•13mo ago

I think it does not answer my question I mean I need smth like Either maybe

Zendist•13mo ago

language-ext has some things like this if you prefer FP: https://github.com/louthy/language-ext The language doesn't have it by default (yet). What you're looking for is a discriminated union, right?

GitHub

GitHub - louthy/language-ext: C# functional language extensions - a...

C# functional language extensions - a base class library for functional programming - GitHub - louthy/language-ext: C# functional language extensions - a base class library for functional programming

Zendist•13mo ago

Or tagged union, depending on which FP circles you identify with.

Thinker•13mo ago

There's a million either/option/DU libraries out there. LanguageExt is cool although a bit intrusive to the average C# workflow. There's also OneOf which is a pretty solid either implementation. You could also make your own, they're not too difficult to implement, and with a few helper methods it's pretty workable.

public readonly struct Either<TA, TB>
{
    private readonly T1? a;
    private readonly T2? b;
    private bool isA;
    private bool isB;

    public T1 A => isA ? a : throw new InvalidOperationException("Value isn't A.");
    public T2 B => isB ? b : throw new InvalidOperationException("Value isn't B.");

    public Either(TA a)
    {
        this.a = a;
        b = default;
        isA = true;
        isB = false;
    }

    public Either(TB b)
    {
        a = default;
        this.b = b;
        isA = false;
        isB = true;
    }
}

public readonly struct Either<TA, TB>
{
    private readonly T1? a;
    private readonly T2? b;
    private bool isA;
    private bool isB;

    public T1 A => isA ? a : throw new InvalidOperationException("Value isn't A.");
    public T2 B => isB ? b : throw new InvalidOperationException("Value isn't B.");

    public Either(TA a)
    {
        this.a = a;
        b = default;
        isA = true;
        isB = false;
    }

    public Either(TB b)
    {
        a = default;
        this.b = b;
        isA = false;
        isB = true;
    }
}

or if you fancy records and better pattern matching capabilities

public abstract record Either<TA, TB>
{
    public sealed record A(TA value) : Either<TA, TB>;
    public sealed record B(TB value) : Either<TA, TB>;
}

public abstract record Either<TA, TB>
{
    public sealed record A(TA value) : Either<TA, TB>;
    public sealed record B(TB value) : Either<TA, TB>;
}

SWEETPONY•13mo ago

thanks, guys that is what I needed

Zendist•13mo ago

I like how concise the abstract record is. Can you show an example of usage?

Thinker•13mo ago

with a couple helper/extension methods and implicit conversions

public abstract record Either<TA, TB>
{
    public sealed record A(TA Value) : Either<TA, TB>;
    public sealed record B(TB Value) : Either<TA, TB>;

    public static implicit operator Either<TA, TB>(TA value) => new A(value);
    public static implicit operator Either<TA, TB>(TB value) => new B(value);

    public Either<TResult, TB> MapA<TResult>(Func<TA, TResult> f) => this switch
    {
        A a => f(a.Value),
        B b => new Either<TResult, TB>.B(b.Value),
    };

    public Either<TA, TResult> MapA<TResult>(Func<TB, TResult> f) => this switch
    {
        A a => new Either<TA, TResult>.A(b.Value),
        B b => f(b.Value),
    };

    public T Match<T>(Func<TA, T> ifA, Func<TB, T> ifB) => this switch
    {
        A a => ifA(a.Value),
        B b => ifB(b.Value),
    };
}

public abstract record Either<TA, TB>
{
    public sealed record A(TA Value) : Either<TA, TB>;
    public sealed record B(TB Value) : Either<TA, TB>;

    public static implicit operator Either<TA, TB>(TA value) => new A(value);
    public static implicit operator Either<TA, TB>(TB value) => new B(value);

    public Either<TResult, TB> MapA<TResult>(Func<TA, TResult> f) => this switch
    {
        A a => f(a.Value),
        B b => new Either<TResult, TB>.B(b.Value),
    };

    public Either<TA, TResult> MapA<TResult>(Func<TB, TResult> f) => this switch
    {
        A a => new Either<TA, TResult>.A(b.Value),
        B b => f(b.Value),
    };

    public T Match<T>(Func<TA, T> ifA, Func<TB, T> ifB) => this switch
    {
        A a => ifA(a.Value),
        B b => ifB(b.Value),
    };
}

public Either<User, string> GetUser(int id)
{
    if (db.UserExists(id)) return db.GetUser(id);
    else return "user does not exist";
}

public Either<User, string> GetUser(int id)
{
    if (db.UserExists(id)) return db.GetUser(id);
    else return "user does not exist";
}

var user = GetUser(id);
var username = user.MapA(user => user.Username);

Console.WriteLine(username.Match(
    ifA: username => username,
    ifB: error => $"GetUser returned an error: {error}"));

var user = GetUser(id);
var username = user.MapA(user => user.Username);

Console.WriteLine(username.Match(
    ifA: username => username,
    ifB: error => $"GetUser returned an error: {error}"));

This has a lot of room for improvement but imo it's the nicest you'll probably get Unfortunately C#'s type inference isn't powerful enough to make this like... actually nice. You run into a lot of annoyances really quickly when you try doing something like this. If you look at for instance Rust then you'll find language features (besides just plain DU support) which make things like this really good.

SWEETPONY•13mo ago

looks good, thanks for explanation I will try to use this

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✅ Is it possible to use union type in C#?