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Union types in C# 15

devblogs.microsoft.com

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Re: Union types in C# 15

#101

Post by dasyatidprime »

merb wrote: post #91
tialaramex wrote: post #75

I don't love OneOrMore 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.

OneOrMore is more or less an example from the functional world. i.e.: 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…

The NonEmptyList in Cats is a product (struct/tuple) type, though; I assume the Haskell version is the same. The type shown in the blog post is a sum (union) type which can contain an empty enumerable, which contradicts the name OneOrMore. The use described for the type in the post (basically a convenience conversion funnel) is different and makes sense in its own right (though it feels like kind of a weak use case). I'm not sure what a good name would've been illustratively that would've been both accurate and not distracting, though.

Re: Union types in C# 15

#102

Post by jayd16 »

FrustratedMonky wrote: post #99
jayd16 wrote: post #93

Earlier quoted context omitted.

Purity is overrated. C# is a kitchen sink language but you need give credit to the language designers. Compared to C++, for example, C# feels feature rich and consistent even though it abandons purity.

I think purity matters where you can have the compiler catch problems.

C# has fantastic tooling, though. Its a hidden feature but to the credit of the language designers, I don't think they often abandon compiler features for dev features.

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.

Re: Union types in C# 15

#103

Post by paulddraper »

tialaramex wrote: post #75

I don't love OneOrMore 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.

I went to prove you wrong…

And you’re exactly right.

It’s not “one or more.”

It’s “one or not one.”

Need two or not two.

Re: Union types in C# 15

#104

Post by recursive »

paulddraper wrote: post #103
tialaramex wrote: post #75

I don't love OneOrMore 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.

I went to prove you wrong… And you’re exactly right. It’s not “one or more.” It’s “one or not one.” Need two or not two.

Hotdog or not hotdog.

Re: Union types in C# 15

#105

Post by sakopov »

gib444 wrote: post #21

Is C# a great language trapped in a terrible ecosystem? ie would masses use C# if it existed in another ecosystem? 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)

Why is the ecosystem bad? I haven't ran any .net code on anything but Linux in years. The open source community is great. I don't know why it gets a bad rep.

Re: Union types in C# 15

#106

Post by amluto »

Hmm, they seem to have chosen to avoid names to the choices in the union, joining C++ variants and (sort of) TypeScript unions: unions are effectively just defined by a collection of types.

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.

Re: Union types in C# 15

#107

Post by mrsmrtss »

jayd16 wrote: post #97
NanoCoaster wrote: post #20

Earlier quoted context omitted.

Absolutely agree. Modern C# language design feels very much lacking in vision or direction. It's mostly a bunch of shiny-looking language features being bolted on, all in ways that make the language massively more complex. 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.…

> Try teaching someone C# nowadays 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...

Exactly, we have had many interns with zero C# experience become fluent in a couple of months and those with prior TypeScript or Java experience get there even faster. A good IDE (like Rider) helps also.

Re: Union types in C# 15

#109

Post by ux266478 »

delta_p_delta_x wrote: post #95
gib444 wrote: post #21

Is C# a great language trapped in a terrible ecosystem? ie would masses use C# if it existed in another ecosystem? 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)

> terrible ecosystem .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…

> but sadly it is saddled with the perception that it is Windows-only, which hasn't been true for a decade

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.

Re: Union types in C# 15

#110

Post by cobbal »

_old_dude_ wrote: post #8
98347598 wrote: post #5

It's very disappointing that they aren't supporting Rust-style discriminated unions.

In C#, all instances have a class, so there is already a discriminant, the class itself. In the article, the example with the switch works because it switches on the class of the instance.

Null doesn't. `union(Int?, String?)` will only have 1 type of null, unlike a proper discriminated union.
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