reactive/Rx.NET/Source/src/System.Reactive/Linq/Observable/IsEmpty.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;

namespace System.Reactive.Linq.ObservableImpl
{
    class IsEmpty<TSource> : Producer<bool>
    {
        private readonly IObservable<TSource> _source;

        public IsEmpty(IObservable<TSource> source)
        {
            _source = source;
        }

        protected override IDisposable Run(IObserver<bool> observer, IDisposable cancel, Action<IDisposable> setSink)
        {
            var sink = new _(observer, cancel);
            setSink(sink);
            return _source.SubscribeSafe(sink);
        }

        class _ : Sink<bool>, IObserver<TSource>
        {
            public _(IObserver<bool> observer, IDisposable cancel)
                : base(observer, cancel)
            {
            }

            public void OnNext(TSource value)
            {
                base._observer.OnNext(false);
                base._observer.OnCompleted();
                base.Dispose();
            }

            public void OnError(Exception error)
            {
                base._observer.OnError(error);
                base.Dispose();
            }

            public void OnCompleted()
            {
                base._observer.OnNext(true);
                base._observer.OnCompleted();
                base.Dispose();
            }
        }
    }
}