Standard FixedArray types in BCL?

[xoofx]

Hey, ☺️

I have been using InlineArray quite extensively in the past months and I love it! Though, one point of difficulty is the fact that it forces to create custom types for a specific kind of array (e.g array of int[4]) which limits the interoperability between libraries.

For example, recently I had to roll out my own set of FixedArray#<T> to be able to use the same type across the different C/C++ interop libraries developed in this project.

A broader related issue is:

• Feature Proposal: Const Generics #89730

But this goes into more difficult territories to get it right language and runtime wise...

So, I'm wondering if having such a type (FixedArray#<T>) builtin in the BCL would be easier to bring (up to e.g 1024 elements, that's the point that is problematic without const literal generic) down into a namespace or a static type (System.FixedArrays) that would not pollute too much the existing namespaces?

Thoughts?

[dotnet-policy-service]

Tagging subscribers to this area: @dotnet/area-system-runtime
See info in area-owners.md if you want to be subscribed.

[RenderMichael]

This sounds like the perfect scenario for const generics #89730

[colejohnson66]

As you mentioned, const generics are probably coming in .NET 9. Why would your proposed FixedArrayN<T> be any better than a generic Array<T, N>? Adding a thousand FixedArrayN<T> types to the runtime seems a bit excessive.

[xoofx]

As you mentioned, const generics are coming in .NET 9

Oh, where was this announced? I didn't say that they are coming but was actually assuming not anytime soon. It's tagged as milestone on the other issue that I missed, but not sure there is someone taking the lead to challenge it. If that is really coming, yes, that issue can be closed

[EgorBo]

As you mentioned, const generics are probably coming in .NET 9

There are no plans for them in any version so far, but, perhaps, issues like this will help to move the needle eventually

[colejohnson66]

Well, #89730 is tagged with the .NET 9 milestone.

[xoofx]

Well, #89730 is tagged with the .NET 9 milestone.

When an issue is tagged for a milestone, it just means that it might be evaluated for this milestone, not that it is going to be done. From Egor's comment that is working closely with folks in the .NET teams, it doesn't look like it's coming.