.NET 10

Apart from [the equivalent of] records, I see nothing big.

Except...

this '''let! a = fetchA() and! b = fetchB()''' really puzzles me. Does C# have a high-level syntax for concurrency timing? [something that Java is strongly lacking, and that Typescript did solve with Promise.all(), which is an ugly syntax, from my perspective]

Any elaboration on this is very welcome.

The code snippet is in F#. And F# has so called "computation expressions".

I think thats F# not C#

Here `a` and `b` can have different types:

    let! a = fetchA() and! b = fetchB()

Whereas `Promise.all` usually requires all promises to have the same type (returning a `List<T>` or even a `List<obj>`) .

See https://learn.microsoft.com/en-us/dotnet/fsharp/whats-new/fs...

The inlining and escape analysis changes are fairly big from a performance perspective.

Also, C# doesn't need nearly as many massive changes like project Valhalla because they got a lot of those design choices right from day 1 (mostly by looking at what Java did that was dumb and avoiding it).

Actually, TypeScript's `Promise.all` can handle different types too.

    const [a, b] = await Promise.all([fetchA(), fetchB()]); // => a: A, b: B

I am talking about C# / F# context where the lists must have homogeneous types.

That TypeScript supports this is yet more complexity introduced to cover usages of an API not designed around types.

As others point out, that's F#, but yes C# has `async`/`await`, and has all the `Promise` methods, just under the `Task` class instead (and with slightly different names/calling conventions through out).