namespace System.Reactive.Linq.ObservableImpl { internal sealed class SumDouble : Producer<double, SumDouble._> { internal sealed class _ : IdentitySink<double> { private double _sum; public _(IObserver<double> observer) : base(observer) { } public override void OnNext(double value) { _sum += value; } public override void OnCompleted() { ForwardOnNext(_sum); ForwardOnCompleted(); } } private readonly IObservable<double> _source; public SumDouble(IObservable<double> source) { _source = source; } protected override _ CreateSink(IObserver<double> observer) { return new _(observer); } protected override void Run(_ sink) { sink.Run(_source); } } }