reactive/AsyncRx.NET/System.Reactive.Async/System/Reactive/Linq/Operators/Range.cs

// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the Apache 2.0 License.
// See the LICENSE file in the project root for more information. 

using System.Reactive.Concurrency;

namespace System.Reactive.Linq
{
    partial class AsyncObservable
    {
        public static IAsyncObservable<int> Range(int start, int count) => Range(start, count, TaskPoolAsyncScheduler.Default);

        public static IAsyncObservable<int> Range(int start, int count, IAsyncScheduler scheduler)
        {
            var max = ((long)start) + count - 1;

            if (count < 0 || max > int.MaxValue)
                throw new ArgumentOutOfRangeException(nameof(count));

            if (scheduler == null)
                throw new ArgumentNullException(nameof(scheduler));

            return Create<int>(observer => scheduler.ScheduleAsync(async ct =>
            {
                ct.ThrowIfCancellationRequested();

                for (int i = start, end = start + count - 1; i <= end && !ct.IsCancellationRequested; i++)
                {
                    await observer.OnNextAsync(i).RendezVous(scheduler);
                }

                ct.ThrowIfCancellationRequested();

                await observer.OnCompletedAsync().RendezVous(scheduler);
            }));
        }
    }
}