namespace System.Reactive.Linq.ObservableImpl { internal sealed class SumInt64 : Producer<long, SumInt64._> { internal sealed class _ : IdentitySink<long> { private long _sum; public _(IObserver<long> observer) : base(observer) { } public override void OnNext(long value) { checked { try { _sum += value; } catch (Exception error) { ForwardOnError(error); } } } public override void OnCompleted() { ForwardOnNext(_sum); ForwardOnCompleted(); } } private readonly IObservable<long> _source; public SumInt64(IObservable<long> source) { _source = source; } protected override _ CreateSink(IObserver<long> observer) { return new _(observer); } protected override void Run(_ sink) { sink.Run(_source); } } }