Could we have Observable.FromCompletionSource

[Thaina]

We could just wrap around callback function and the like easily by wrapping CompletionSource

static class Observable
{
    static Observable<T> FromCompletionSource<T>(Action<AwaitableCompletionSource<T>> action)
    {
        return Observable.FromAsync(async(token) => {
            var source = new AwaitableCompletionSource<T>();
            action(source);
            return await source.Awaitable;
        });
    }
    
    static Observable<T> FromCompletionSource<T>(Action<TaskCompletionSource<T>> action)
    {
        return Observable.FromAsync(async(token) => {
            var source = new AwaitableCompletionSource<T>();
            action(source);
            return await source.Task;
        });
    }
}

Usage

void DoSomething(string uid,Action<List<string>> onSuccess,Action<Exception> onFailure);

////

Observable.FromCompletionSource<List<string>>((source) => DoSomething("123456"),source.SetResult,source.SetException);