Official proposal for Type Unions in C#

Post by SideburnsOfDoom » Thu, Aug 08, 2024, 11:45 AM UTC

zarathustreal wrote: post #156

SideburnsOfDoom wrote: post #87

Earlier quoted context omitted.

> I don't think "type union" is a term of the art "sum type" is the term of art in Computer Science theory, but "union type" is also used. See https://en.wikipedia.org/wiki/Type_theory#Sum_type https://en.wikipedia.org/wiki/Tagged_union

At this point, calling it by its correct name (Sum Types) would leave them looking stupid for not using the correct name (Product Types) for their “records”

Post by ctenb » Thu, Aug 08, 2024, 12:00 PM UTC

kbgart wrote: post #161

Eji1700 wrote: post #4

Earlier quoted context omitted.

F# is so hard to walk back from. I wish Microsoft would support it better and actually push it, because it's such a perfect sweet spot. Most of the functional advantages without being shackled to pure functions and the like is so easy to develop in. Instead they've been, very slowly, turning C# into F#, which is even weirder to watch.

Looking at the syntax in the type union proposal, I hope they take a bit more from F#. It really needs some work.

Post by jasomill » Thu, Aug 08, 2024, 12:13 PM UTC

cies wrote: post #221

jcparkyn wrote: post #216

Earlier quoted context omitted.

But then what name would they use for tuples, which are distinct from records?

both tuples and record (structs) are product types. tuples are "untagged", records/structs are "tagged" (the members have names). sum types also have tagged and untagged variants. the untagged variants are less useful (more cumbersome) in case of sum types and hence often are not implemented in languages.

  var p = (x: 1, y: 2);
  var q = (u: 1, y: 2);
  var f = ((int x, int y) a) => a.x + a.y;

  p == q 
  f(p) == 3
  f(q) == 3
  p.GetType() == q.GetType()

  var r = q.x;

  dynamic d = q;

  var s = d.u;

Post by Akronymus » Thu, Aug 08, 2024, 1:04 PM UTC

mattmanser wrote: post #139

bbkane wrote: post #119

Earlier quoted context omitted.

Does C# impose a lot of organization? I've only worked in one C# codebase but it has partial classes everywhere and TONs of abstraction bloat. I found it difficult to reason about the organization.

C# doesn't really, but VS + the asp.net framework do. You kinda have to fight against the IDE to not do a lot of things a certain way. For example, it'll automatically namespace new files according to your folder structure. They've also turned a certain amount of automatic linting on to gently suggest/nag you to write in a particular way.Suggest you write classes in certain ways, use newer language features, declare…

Post by jasomill » Thu, Aug 08, 2024, 1:14 PM UTC

zamalek wrote: post #2

> The interior layout of the union struct is chosen to allow for efficient storage of the data found within the different possible member types with tradeoffs between speed and size chosen by the compiler. Having _attempted_ (and being bitten by) far too much black magic with C# unions in the past (using FieldOffset), there is an unfortunate situation here: aliasing a pointer/ref value and value is UB. This means tha…

  using System.Runtime.InteropServices;
  var s = new S { Bar = "Baz" };
  [StructLayout(LayoutKind.Explicit)]
  public struct S {
      [FieldOffset(0)] public UInt64 Foo;
      [FieldOffset(0)] public Object Bar;
  }