Other languages have unions with named choices, where each name selects a type and the types are not necessarily all different. Rust, Haskell, Lean4, and even plain C unions are in this category (although plain C unions are not discriminated at all, so they’re not nearly as convenient).
I personally much prefer the latter design.
I've seen exactly one Rust type which is actually a union, and it's a pretty good justification for the existence of this feature, but one isn't really enough. That type is MaybeUninit<T> which is a union of a T and the empty tuple. Very, very, clever and valuable, but I didn't run into any similarly good uses outside that.
That is essentially the motivation, primarily in the context of FFI where matching C's union behaviour using transmute is tricky and error-prone.
It's trying to generalize - we might have exactly one T, fine, or a collection of T, and that's more T... except no, the collection might be zero of them, not at least one and so our type is really "OneOrMoreOrNone" and wow, that's just maybe some T.
If I understand correctly, it’s actually OneOrOneOrMoreOrNone. Because you have two distinguishable representations of “one”.
The only reason to use this would be if you typically have exactly one, and you want to avoid the overhead of an enumeration in that typical case. In other words, AnyNumberButOftenJustOne<T>.
https://hackage.haskell.org/package/oneormore or scala: https://typelevel.org/cats/datatypes/nel.html
it's for type purists, because sometimes you want the first element of the list but if you do that you will get T? which is stupid if you know that the list always holds an element, because now you need to have an unnecessary assertion to "fix" the type.
You are free to call it `public union Some<T>(T, IEnumerable<T>)`
So IEnumerable<T> ? What's up with wrapping everything into fancy types just to arrive at the exact same place.
And you’re exactly right.
It’s not “one or more.”
It’s “one or not one.”
Need two or not two.
The problem with ad-hoc unions is that without discipline, it invariably ends in a mess that is very, very hard to wrap your head around and often requires digging through several layers to understand the source types.
In TS codebases with heavy usage of utility types like `Pick`, `Omit`, or ad-hoc return types, it is often exceedingly difficult to know how to correctly work with a shape once you get closer to the boundary of the application (e.g. API or database interface since shapes must "materialize" at these layers). Where does this property come from? How do I get this value? I end up having to trace through several layers to understand how the shape I'm holding came to be because there's no discrete type to jump to.
This tends to lead to another behavior which is lack of documentation because there's no discrete type to attach documentation to; there's a "behavioral slop trigger" that happens with ad-hoc types, in my experience. The more it gets used, the more it gets abused, the harder it is to understand the intent of the data structures because much of the intent is now ad-hoc and lacking in forethought because (by its nature) it removes the requirement of forethought.
"I am here. I need this additional field or this additional type. I'll just add it."
So even when I write TS and I have the option of using ad-hoc types and utility types, I almost always explicitly define the type. Same with types for props in React, Vue, etc; it is almost always better to just explicitly define the type, IME. You will thank yourself later; other devs will thank you.
Are you sure? This is a feature of OCaml but not F# IIUIR
Edit: https://github.com/fsharp/fslang-suggestions/issues/538
Yes and no. C# unions aren’t sealed types, that’s a separate feature. But they are strictly nominal - they must be formally declared:
union Foo(Bar, Baz);
Bar | Baz
> unions enable designs that traditional hierarchies can’t express, composing any combination of existing types into a single, compiler-verified contract.
To me that "compiler-verified" maps to "sealed", not "on the fly". Probably.
Their example is:
public union Pet(Cat, Dog, Bird);
Pet pet = new Cat("Whiskers");
- the union type is declared upfront, as is usually the case in c#. And the types that it contains are a fixed set in that declaration. Meaning "sealed" ?
(Dog, Cat) pet = new Cat();
So without defining the union with an explicit name beforehand.
var someUser = new { Name = "SideburnsOfDoom", CommentValue = 3 };
A type can be given at compile-time in a declaration, or generated at compile-time by the compiler like this. But it is still "Compiler-verified" and not ad-hoc or at runtime.
the type (Dog, Cat) pet seems similar, it's known at compile-time and won't change. A type without a usable name is still a type.
Is this "ad-hoc"? It depends entirely on what you mean by that.
=> named sum type implicitly tagged by it's variant types
but not "sealed", as in no artificial constraints like that the variant types need to be defined in the "same place" or "as variant type", they can be arbitrary nameable types
Here is visual layout if anyone is interested - https://vectree.io/c/memory-layout-tagging-and-payload-overl...
* https://devblogs.microsoft.com/dotnet/csharp-15-union-types/...
We have been pushing toward higher performance for years and this is a performance pitfall for unions would are often thought of as being lighter weight than inheritance hierarchies.
F# just stores a field-per-case, with the optimization that cases with the same type are unified which is still type safe.
Active patterns, computation expressions, structural typing, statically resolved type parameters, explicit inlining, function composition, structural equality, custom operators and much richer generators.
Not sure I would want the last thing in C#, I think having boundaries at the function signature for that.
https://github.com/manifold-systems/manifold/tree/master/man...
The only thing I wish now is for someone to build a functional Web framework for C#.
In the article, the example with the switch works because it switches on the class of the instance.
What a missed opportunity. I think really F# if you combine all of its features, and what it left out, was the way. Pulling them all into C# just makes C# seem like a big bag of stuff, with no direction.
F#'s features, and also what it did not included, gave it a style and 'terseness', that still can't really be done in C#.
I don't really get it. Was a functional approach really so 'difficult'? That it didn't continue to grow and takeover.
So far everything that was added to C# very much reduces the amount of dead boilerplate code other languages struggle with.
Really give it an honest try before you judge it based on the summation of headlines.
given that most of the thinks added seem more inspired by other languages then "moved over" from F# the "other languages struggle with" part makes not that much sense
like some languages which had been ahead of C# and made union type a "expected general purpose" feature of "some kind":
- Java: sealed interfaces (on high level the same this C# features, details differ)
- Rust: it's enum type (but better at reducing boilerplate due to not needing to define a separate type per variant, but being able to do so if you need to)
- TypeScript: untagged sum types + literal types => tagged sum types
- C++: std::variant (let's ignore raw union usage, that is more a landmine then a feature)
either way, grate to have it, it's really convenient to represent a `TYPE is either of TYPES` relationship. Which are conceptually very common and working around them without proper type system support is annoying (but very viable).
I also would say that while it is often associated with functional programing it has become generally expected even if you language isn't functional. Comparable to e.g. having some limited closure support.
I honestly have no idea where you would get this idea from. C# is a pretty opinionated language and it's worst faults all come from version 1.0 where it was mostly a clone of Java. They've been very carefully undoing that for years now.
It's a far more comfortable and strict language now than before.
The only things that I wish for are: rusts borrow-checker and memory management. And the AOT story would be more natural.
Besides that, for me, it is the general purpose language.
Yes, C# is a jack of all trades and can be used at many things. Web, desktop mobile, microservices, CLI, embedded software, games. Probably is not fitted for writing operating systems kernels due to the GC but most areas can be tackled with C#.
Midori would like to have a word with you:
Better than a new language for each task, like you have with Go (microservices) and Dart (GUI).
I'm using F# on a personal project and while it is a great language I think the syntax can be less readable than that of C#. C# code can contain a bit too much boilerplate keywords, but it has a clear structure. Lack of parenthesis in F# make it harder to grasp the structure of the code at a glance.
For example, C# chose not to go down the route of type erasure for the sake of generics and because of that you don't get the same sort of runtime type issues that Java might have.
also called general purpose, general style langue
> that still can't really be done in C#
I would think about it more as them including features other more general purpose languages with a "general" style have adopted then "migrating F# features into C#, as you have mentioned there are major differences between how C# and F# do discriminated sum types.
I.e. it look more like it got inspired by it's competition like e.g. Java (via. sealed interface), Rust (via. enum), TypeScript (via structural typing & literal types) etc.
> Was a functional approach really so 'difficult'?
it was never difficult to use
but it was very different in most aspects
which makes it difficult to push, sell, adapt etc.
that the maybe most wide used functional language (Haskel) has a very bad reputation about being unnecessary complicated and obscure to use with a lot of CS-terminology/pseudo-elitism gate keeping doesn't exactly help. (Also to be clear I'm not saying it has this properties, but it has the reputation, or at least had that reputation for a long time)
Probably more this than any technical reason. More about culture and installed view points.
I don't want to get into the objects/function wars, but do think pretty much every technical problem can be solved better with functions. BUT, it would take an entire industries to re-tool. So think it was more about inertia.
Inertia won.
Just look at this feature: https://learn.microsoft.com/en-us/dotnet/csharp/whats-new/cs...
Was this needed? Was this necessary? It's reusing an existing keyword, fine. It's not hard to understand. But it adds a new syntax to a language that's already filled to the brim, just to save a few keystrokes?
Try teaching someone C# nowadays. Completely impossible. Really, I wish they would've given F# just a tenth of the love that C# got over the years. It has issues but it could've been so much more.
Do you actually have a datapoint of someone failing to understand C# or are you just hyperbolically saying its a big language? The tooling, the ecosystem, the linting, the frameworks. Its a very easy language to get into...
For you it may be fine to write:
List<string> strs = new List<string>();
And sure if you have been using C# for years you know all the things going on here.
But it shouldn’t be an argument that:
List<string> strs = [];
Is substentionally easier to grasp.
And that has been the theme of all changes.
The example you point out is the advanced case, someone only needs in a very specific case. It does not have a lot todo with learning the language.
The language design team is really making sure that the features work well throughout and I think that does deserve some credit.
I agree that = [] is perfectly fine syntax. But I would definitely argue that:
[with(capacity: values.Length * 2), ..
is non-intuitive and unnecessary. What other language is there that has this syntax? Alternatively, is this a natural way of writing this? I wouldn't say so.
My main language in my free time is Rust, a few years ago it was F#. So, I'm absolutely open to other syntax ideas. But I feel that there has to be a direction, things have to work together to make a language feel coherent.
Another example would be Clojure, which I started learning a few months ago (before we all got swept up in AI FOMO :D). Clojure as a language feels very coherent, very logical. I'm still a beginner, but every time I learn something about it, it just makes sense. It feels as if I could have guessed that it works this way. I don't get that feeling at all in many of the new features of C#.
> The example you point out is the advanced case, someone only needs in a very specific case. It does not have a lot todo with learning the language.
I disagree. When learning the language, you're going to have to read other people's code and understand it. It's the same basic principle, but, I'd argue, much worse in C++. Yes, in theory, you don't have to understand SFINAE and template metaprogramming and (now) concepts and all those things. You could just work in a subset of C++ that doesn't use those things. But in practice, you're always going to have issues if you don't.
https://docs.python.org/3/tutorial/datastructures.html#list-...
I'm also not sure that something not being intuitive or natural is necessarily a bad thing in of itself. You state it as if it's so, but you haven't demonstrated that this way of defining a list is worse. You also haven't made any attempt to understand any possible benefit, nor have you attempted any sort of analysis comparing the good and the bad aspects.
> I'm also not sure that something not being intuitive or natural is necessarily a bad thing in of itself. You state it as if it's so, but you haven't demonstrated that this way of defining a list is worse.
I would argue that a language having more features, without the feature being helpful, is a bad thing in itself. If the syntax isn't necessary or very convenient in many cases, it shouldn't exist. The syntax being natural (which, absolutely, is a very subjective thing) just makes it less of an issue, I'd say.
Every new syntax added to the language adds cognitive overhead to readers of code. But also, it adds possible interactions with other language features that may be added in the future. Now, the example I brought up doesn't really concern the second point, I'll concede that. But unions? That is a big concept to add to a language that already has decades of existing conventions and tons of other features. How will they interact with generics? Nullable reference types? And, just as importantly: How will they interact with any other features that might be added at some point that we don't even know about?
I'm not against adding syntax sugar. For example, I quite like primary constructors, which is another relatively new C# feature. I think it's a bit annoying that they were kind of added in a roundabout way, by first adding records and then adding primary constructors to classes, but this time they don't define properties but fields...but in the end, it's a nice convenience feature when using constructor injection. Which, whatever one may feel about this, is pretty common in C# code.
But the thing is: If every single feature that's nice for a few use cases gets added to a language, the language will explode. The best example for this is C++. C# is definitely not that bad, far from it, but my point is that I want it to stay that way :)
Dictionary<string, List<Tuple<string, string>>> foo = new Dictionary<string, List<Tuple<string, string>>>
Dictionary<string, List<Tuple<string, string>>> foo = DoSomeWork();
No-one wants to go back to that, and anyone who says C# is over-complicated I think is forgetting how rough it was in the earliest versions.
While introduction of auto-typing through "var" helped a lot with that, you'd still regularly have to fight if you wanted to properly initialise arrays with values, because the syntax was just not always obvious.
Collection literals are amazing, and now the ability to pass things into the constructor means they can be used when you need constructor parameters too, that's just a good thing as you say.
This is exactly how C++ landed where it is now. Every time it's "you only need to know that syntax if..." well it ends up everyone has to know that syntax because someone will use it and if you're a responsible programmer you'll end up reading a lot code written from other people.
But still there is a difference between learning and mastering.
I recently helped my partner learn for her CS class, and I feel very comfortable arguing that my previous statement holds up.
Mastering? No, in that case I agree with you.
If they actually put effort in F#, it would have reached "unteachable" state already :)
I would've loved an F# that found a way to improve on the performance issues, especially when using computation expressions. That and, either, a deeper integration of .NETs native OOP subtyping, or some form of OCaml-like module system, would have been enough to make it an almost perfect language for my tastes.
Obviously, these are big, and maybe impossible, issues. But Microsoft as a whole never really dedicated enough resources to find out. I feel for the people still working on it, their work is definitely appreciated :)
So is it a F# issue or inherent to functional programming?
Looking at it, the MS docs contain something about this exact topic, so maybe it's better nowadays: https://learn.microsoft.com/en-us/dotnet/fsharp/language-ref...
Sadly, I haven't used F# for years at this point so I can't speak to the current state.
That isn't a reasonable take. Failing to teach a language by enumerating all its features is an indictment of the instructor and not the language.
You're right, it's not impossible and in general it's not among the hardest languages to teach. But I would argue, it is heading that way.
There are already so many ways to do things in C#. For example, try explaining the difference between fields and properties; sounds easy, but making it really stick is quite a challenge. And that's one of the simplest cases (and a feature I'm 100% in favor of).
And you will have to explain it at some point, because real codebases contain these features so at some point, it'll need to be taught. Learning a language doesn't stop when you can write a simple application, it continues up until at least you're comfortable with most of its features and their practical use. The quicker one can get people to that point, the easier the language is to teach, I'd argue.
One might also argue that learning never really stops, but that's beside the point :)
In general, my issue isn't any specific feature. C# has many features that are non-trivial to learn but still great: value types, generics, expression trees. Source generators are relatively new and I like them! I like most of the things they're doing in the standard library or the runtime. Spans everywhere is a nice improvement, most new APIs are sensible and nice to use and the runtime just keeps getting faster every release. Great. It's more the pure C# language side I have an issue with.
But every language has a budget of innovation and cognitive load that you can expect people to deal with, and C# is not using its budget very wisely in my opinion.
> I don't really get it
It does each reasonably well (with web APIs being where I think they truly shine).
> Was a functional approach really so 'difficult'
But I do agree. C# is heading to a weird place. At first glance C# looks like a very explicit language, but then you have all the hidden magical tricks: you can't even tell if a (x) => x will be a Func or Expression[0], or if a $"{x}"[1] will actually be evaluated, without looking at the callee's signature.
[0]: https://learn.microsoft.com/en-us/dotnet/csharp/advanced-top...
[1]: https://learn.microsoft.com/en-us/dotnet/csharp/advanced-top...
In the places where that is a thing, I've never needed to care. (Which is kind of the point)
Note that most of its development is still by the open source community and its tooling is an outsider for Visual Studio, where everything else is shared between Visual Basic and C#.
With the official deprecation of VB, and C++/CLI, even though the community keeps going with F#, CLR has changed meaning to C# Language Runtime, for all practical purposes.
Also UWP never officially supported F#, although you could get it running with some hacks.
Similarly with ongoing Native AOT, there are some F# features that break under AOT and might never be rewritten.
A lost opportunity indeed.
Not adding functional features to F# doesn't mean F# would have gained more usage. And if someone wants to use F#, no one is stopping him or her.
But, that would takes, schools changing, companies changing, everything. So it was really the installed base that won, not what was better.
We'd have to go back in time, and have some ML Language win over C++ .
Agreed. Java is on the same trail.
I work much with C# these days and wish C# had as cohesive a syntax story. It often feels like "island of special syntax that makes you fall of a cliff".
Or is it becoming a ball-of-mud/bad language compared to its contemporaries?
(Honest questions. I have never used .NET much. I'm curious)
Are there particular things about the ecosystem that you worry about (or have heard about)? Biggest complaint I would have is that it seems like many popular open source libraries in the .NET ecosystem decide to go closed source and commercial once they get popular enough.
(The amount of times I hear "the standard lib is great!" seems more to attempt to defend the plethora of commercial libraries, more than anything)
The community feels rather insular too? The 9-5 dayjob types with employers who don't understand or embrace open source? At my age I can respect that though
And is Postgresql a 2nd-class citizen? If so, your boss will tell you to use SQL Server surely?
I guess it's hard to get a grasp on the state/health of .NET as to me it seems 99.99999% of the code is in private repos companies, as it's not a popular choice for open source projects. Which itself seems like a proxy signal though
It is what it is but I wouldn't say its actually the fault of the language, especially now.
> And is Postgresql a 2nd-class citizen?
Microsoft maintains the Npgsql project[0] and I say that it is a very capable, feature rich adapter.
I have not used C# with SQL Server in almost a decade.
It serves many audiences so it can feel like the language is a jack of all trades and master of none (because it is) and because it is largely backwards compatible over its 20+ years of existence.
That said, I think people make a mountain out of a molehill with respect to keyword sprawl. Depending on what you're building, you really only need to focus on the slice of the language and platform you're working with. If you don't want to use certain language features...just don't use them?
I think it excels in a few areas: web APIs and EF Core being possibly the best ORM out there. For me, it is "just right". Excellent platform tooling, very stable platform, very good performance, hot reload (good, but not perfect), easy to pick up the language if you already know TypeScript[1]; there are many reasons it is a good language and platform.
[0] https://learn.microsoft.com/en-us/dotnet/csharp/advanced-top...
That's why I like it so much. And now, I can write mostly functional code.
>I think it excels in a few areas: web APIs and EF Core being possibly the best ORM out there
It's awesome for web stuff and microservices.
> It's awesome for web stuff and microservices.
Is it good at the wrong thing? Eg compare to strongly-typed query generators
> Is it good at the wrong thing?
.NET is a fantastic ecosystem. Has a decent build and dependency system (NuGet, dotnet run/build, declarative builds in XML). Massive standard library, with a consistent and wide focus on correctness, ergonomics, and performance across the board.
You can write everything in many languages, all on the same runtime: business logic in C#; hot paths interfacing with native libraries in C++/CLI; shell wrappers in PowerShell, document attachments with VB, data pipelines in F#.
I feel more people should use it, or at least try it, but sadly it is saddled with the perception that it is Windows-only, which hasn't been true for a decade (also, IMO, not necessarily a negative, because Windows is a decent OS, sue me).
In my experience it does not work very well outside of the sanctioned Linux distributions. Quirky heisenbugs and nonsensical crashes made it virtually unusable for me on Void. I doubt that's changed in the years that have since passed.
> not necessarily a negative, because Windows is a decent OS
Is a language runtime worth an operating system? I think that's a paradigm we left behind in the 1970s when the two were effectively inseperable (and interwoven with hardware!) I wouldn't expect someone to swap to using a Unix system because they really want a better Haskell experience.
I just don't see any actual interesting or meaningful reasons to care about .NET, I effectively feel the same way about it that I do about Go. Just not something that solves any problem I have, and doesn't have anything that interests me. Although effectively I did try it, so it's a moot point considering that's one of the outcomes you're wishing for.
It has a bad rep because Microsoft could Microsoft as they do.