Wow 2016 would have loved this news.
.NET (OK, C#) finally gets union types
81–90 of 300 posts
Re: .NET (OK, C#) finally gets union types
#82C# is my strongest and favorite language. That said, it's frustrating that the C# framework ecosystem lacks solid options. MAUI is especially half-baked, and I'm really starting to doubt whether I should continue using XAML
C# used to be my favorite language, but having spent a lot of time in Rust using its algebraic data types + match statements + Option & Result types, then returning to C# to build a few moderately involved libraries, I'm horrified by the enums and null & error handling that I used to deal with all the time. I knew that enums were really just named integer values and nothing more, but I had forgotten than you can buil…
[dead]
Re: .NET (OK, C#) finally gets union types
#83I wish the syntax looked more like typescript. This will confuse my eyes for a while.
It works quite differently from TypeScript, so the syntax used there wouldn't have worked.
Re: .NET (OK, C#) finally gets union types
#84C# is my strongest and favorite language. That said, it's frustrating that the C# framework ecosystem lacks solid options. MAUI is especially half-baked, and I'm really starting to doubt whether I should continue using XAML
Winforms is better than ever. You can use it with .NET10 and WebView2 is a thing now.
Re: .NET (OK, C#) finally gets union types
#85Earlier quoted context omitted.
Alright. I'm actually fine with WinForms and WPF since my factory floor codes depend on them. But the reality is they aren't expressive enough for modern UIs. XAML is an issue, and WPF is boilerplate hell. But then Blazor is too heavy, MAUI is broken and buggy, Avalonia is underwhelming, and WinUI 3 is an absolute nightmare.
> Avalonia is underwhelming How? Can you elaborate?
Not OP, but I've found Avalonia to be pretty much a direct replacement for WinForms. I mean that both as a compliment and a deserved insult. It's not the WinForms we wanted, but it is the one we deserve.
More seriously, it has all the strengths and weaknesses of WinForms and feels about exactly as unfinished and rough as WinForms. I still have to implement custom widgets that i would have expected to be included out of the box. It's nice that it's cross-platform, though with all the rough edges that cross-platform .net still has. It really, truly feels exactly like every C# UI framework I've ever used in the last 20 years: almost good, not quite finished, and takes an amount of effort that is just unreasonable compared to any other language/framework of any age.
I've been a C# dev for most of my career. I have more fun writing UIs from scratch by drawing individual pixels in C++ than any C# UI.
Re: .NET (OK, C#) finally gets union types
#86C# is my strongest and favorite language. That said, it's frustrating that the C# framework ecosystem lacks solid options. MAUI is especially half-baked, and I'm really starting to doubt whether I should continue using XAML
C# used to be my favorite language, but having spent a lot of time in Rust using its algebraic data types + match statements + Option & Result types, then returning to C# to build a few moderately involved libraries, I'm horrified by the enums and null & error handling that I used to deal with all the time. I knew that enums were really just named integer values and nothing more, but I had forgotten than you can buil…
> I had forgotten than you can build a perfectly legal enum from an integer out of the bounds of the enum's range. And a switch statement is non-exhaustive
These are solved by the new feature described in the article that we're commenting on right now. They're giving us unions and exhaustive switch. Ctrl+F "canonical way to work with unions" in the article to see an example. One of the best parts about C# is they never stop bringing useful features from other languages back home to us in C#. It makes for a large language with a lot of features, but if we really want something, we'll eventually get it in C#.
Re: .NET (OK, C#) finally gets union types
#87Earlier quoted context omitted.
It’s huge in the game dev world, with Unity and Godot. .net also had a reasonable community on mobile for a while thanks to Xamarin, but I cannot imagine that many people using it for new mobile projects in 2026 (outside of game dev I mean). It’s a very decent language (I mean C#) and runtime, I wish it had more market share in the startup world.
Unity is still using Mono these days which is missing basically all of the C# and .NET improvements from the past... 10 years now? Godot was using Mono too but has since switched to .NET in version 4. Still a great language and I hope Unity can hit their target to switch to .NET soon!
Damn, I assumed they had switched to .net core, I cannot believe they are still stuck on mono. Thanks for the correction
Re: .NET (OK, C#) finally gets union types
#88Most people don't know that there are fundamentally two different kinds of "union" types: "tagged unions" and "untagged unions". Now .NET is introducing tagged unions, but unfortunately they stick to the popular tradition of calling them just "unions", which greatly adds to the confusion.
To clarify, these tagged unions are fundamentally different from the untagged unions that can be found in languages like Typescript or Scala 3.
Tagged unions (also called "discriminated unions" or "sum types") are algebraic data types. They act as wrappers, via special constructors, for two (or more) disjoint types and values. So a tagged union acts like a bag that has two (or more) labelled ("tagged") slots, where each slot has exactly one type and exactly one of these slot can take a value.
Untagged unions are set theoretic (rather than algebraic) data types. They don't require wrapping via a special constructor. They behave like the logical OR. They are not disjoint slots of a separate construct. A variable or function x with the type "Foo | Bar" can be of type Foo, or Bar, or both. To access a Foo method on x, one has to first perform a typecheck for Foo, otherwise the compiler will refuse the method call (since x might only have the type Bar which would produce an exception). If a variable is of type A, it is also of type A|B ("A or B"). There are also intersection types (A&B) which indicate that something has both types rather than at least one, and complement/negation types (~A indicates that something is of any type except A). Though the latter are not implemented in any major language so far.
Re: .NET (OK, C#) finally gets union types
#89Earlier quoted context omitted.
Simple example that I use often when writing API clients: In current C# I usually do something like public class ApiResponse { public T? Response { get; set; } public bool IsSuccessful { get; set; } public ErrorResponse Error { get; set; } } This means I have to check that IsSuccessful is true (and/or that Response is not null). But more importantly, it means my imbecile coworkers who never read my documentation need…
I think I get it but I'm not really sure what I'm gaining over exception types. With an intelligent use of exceptions I can easily specify the happy path and all the error paths separately which seems really nice to me, because usually the behaviour between those two outcomes is rather different.
> I think I get it but I'm not really sure what I'm gaining over exception types. With an intelligent use of exceptions I can easily specify the happy path and all the error paths separately which seems really nice to me, ...
Until your coworker comes along and accidentally refactors the code to skip the exception catching and it suddenly blows up prod.
With tagged unions you can't accidentally dereference to the underlying value without checking if it's actually proper data first.
Re: .NET (OK, C#) finally gets union types
#90F# leads the way and C# slowly catches up, as always. Yet for some reason, C# still gets all the mindshare.
I love F#. It's my go-to language and one that I work with every day. Personally I feel that IDE support (as in perf, QoL features, etc.) is the only area it lags behind C#, and outside of that it's a clear winner for everything that I want to do with it.