[API Proposal]: ToObservable and ToAsyncEnumerable()

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Assessment

Difficulty
5/5
Estimated time
Over a week
Newbie friendliness
35/100
Issue type
Feature
Clarity
Mostly clear
Activity status
Quiet
Tech stack
csharp
Domain
api, backend-api-design

Research direction

Start with the proposed System.Linq.AsyncEnumerable API and the linked dotnet/reactive issues 2212 and 2199, then trace the existing IObservable and IAsyncEnumerable conversion behavior. The payload names no repository files or tests; done requires an agreed implementation of both proposed helpers that addresses the cited implementation concerns.

Written by the indexing model from the issue text.

Description

api-suggestion area-System.Linq help wanted
Background and motivation

Both IObservable<T> and IAsyncEnumerable<T> are defined in the runtime,
however the conversion helpers between one and the other are not.

Since System.Linq.Async will be deprecated, these methods need to be defined somehwere else.
In my opinion makes sense to define them here, in a similar way of this DataFlowBlock to IObservable<T> helper.

Note also that current implementations in dotnet/reactive have some serious issues. So it doesn't exist any valid implementation at all at the moment! (See for example this issue on reactive).

See also this.

API Proposal
using System.Collections.Generic;

namespace System.Linq;
public static partial class AsyncEnumerable
{
    public static IAsyncEnumerable<TSource> ToAsyncEnumerable<TSource>(this IObservable<TSource> source);
    public static IObservable<TSource> ToObservable<TSource>(this IAsyncEnumerable<TSource> source);
}
API Usage
using System.Reactive.Linq;
using System.Threading.Channels;

var source = Observable.Timer(TimeSpan.FromSeconds(1));
await foreach (var tick in source.ToAsyncEnumerable())
{
    if (tick == 4) break;
    Console.WriteLine(tick);
}

var numbersChannel = Channel.CreateUnbounded<int>();
IObservable<int> numbersObservable = numbersChannel.Reader
                                                   .ReadAllAsync()
                                                   .ToObservable();
Alternative Designs

No response

Risks

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Dominant language
C#
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