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