namespace System.Reactive.Linq.ObservableImpl { internal sealed class SumInt64Nullable : Producer<long?, SumInt64Nullable._> { internal sealed class _ : IdentitySink<long?> { private long _sum; public _(IObserver<long?> observer) : base(observer) { } public override void OnNext(long? value) { checked { try { if (value.HasValue) _sum += value.Value; } catch (Exception error) { ForwardOnError(error); } } } public override void OnCompleted() { ForwardOnNext(_sum); ForwardOnCompleted(); } } private readonly IObservable<long?> _source; public SumInt64Nullable(IObservable<long?> source) { _source = source; } protected override _ CreateSink(IObserver<long?> observer) { return new _(observer); } protected override void Run(_ sink) { sink.Run(_source); } } }