The indexer syntax on IEnumerable using the extension block is not functioning correctly in .NET 10 Preview 3

[egvijayanand]

public static class Enumerable
{
    extension<TSource>(IEnumerable<TSource> source)
    {
        public TSource this[Index index] => source.ElementAt(index);
    }
}

int[] values = [1, 2, 3];
var items = values.AsEnumerable();
var item = items[0]; // Not working
var item2 = Enumerable.get_Item(items, 0); // Works

Please ensure this is resolved before the stable release.

[HaloFour]

See: https://github.com/dotnet/core/blob/main/release-notes/10.0/preview/preview3/csharp.md#extension-members

As of C# 14 preview 3 only methods and properties have been implemented. Indexers and other member types will come in a future release.

[CyrusNajmabadi]

How can Docs provide info that is not yet released? Doesn't make sense at all.

Docs and work are built concurrently as that is more efficient than forcing it to be done serially. While things are in preview, expecting any sort of strict correctness between the two is not a thing.

[egvijayanand]

Requesting you people to go through the sample provided, the Indexer syntax alone is not working but the direct static invocation is working fine.

It's clear evidence that Indexer is part of this preview release as the underlying get_Item method is generated by the compiler. It's worth mentioning that the Item is the property name for the Indexer.

[CyrusNajmabadi]

Docs follow the work and not the other way around.

No. Docs follow the same schedule we're on. And the final docs are ready one the feature is finally ready. There is no reason during the preview process to have any sort of strange dependency that will simply interfere with the doc writers' ability to order and organize their work.

This is how previews have worked for literally decades. We're not changing it because you don't to see early docs that may refer to things that aren't available to you. That's literally what a preview is. It's a glimpse into the state of things early in development, so it can be played with. That's it.

[CyrusNajmabadi]

is generated by the compiler.

It's a preview. Everything is partially complete with this feature. There is literally no part of it that is done. Even the literal primary areas we want in the hands of users (like methods and properties) have huge parts of them that are still coming.

The way development works is that we stage the different parts of work, and we have branches with that staging that are flowing in at their own schedules. The preview branch that you are using is simply a snapshot of some subsets of work that happened to be ready to make it into that branch for the snap date point. That's it.

The same is true with docs. All of this work is happening concurrently and flowing to the branches when ready. There is no desire or reason to gates any of these flows on other parts, as that simply slows things down and adds more manual effort to things. Instead, we remove dependencies as much as possible, work concurrently, and release snaps at certain points in time to allow people to use things. The only major goal we have is that all the work is done by certain dates, and then everything we want is merged into teh final non-preview builds that will eventually go out.

[CyrusNajmabadi]

Closing as this has been answered. If you want certain capabilities that didn't merge into the release you're using, you can cut a release of roslyn yourself and use the compiler you build. You can then target any of our branches and even try things out in an individual dev's branches as they are literally developing them.