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