namespace System.Reactive.Linq.ObservableImpl { internal sealed class Aggregate<TSource, TAccumulate> : Producer<TAccumulate, Aggregate<TSource, TAccumulate>._> { internal sealed class _ : Sink<TAccumulate>, IObserver<TSource> { private readonly Func<TAccumulate, TSource, TAccumulate> _accumulator; private TAccumulate _accumulation; public _(TAccumulate seed, Func<TAccumulate, TSource, TAccumulate> accumulator, IObserver<TAccumulate> observer, IDisposable cancel) : base(observer, cancel) { _accumulator = accumulator; _accumulation = seed; } public void OnNext(TSource value) { try { _accumulation = _accumulator(_accumulation, value); } catch (Exception error) { _observer.OnError(error); base.Dispose(); } } public void OnError(Exception error) { _observer.OnError(error); base.Dispose(); } public void OnCompleted() { _observer.OnNext(_accumulation); _observer.OnCompleted(); base.Dispose(); } } private readonly IObservable<TSource> _source; private readonly TAccumulate _seed; private readonly Func<TAccumulate, TSource, TAccumulate> _accumulator; public Aggregate(IObservable<TSource> source, TAccumulate seed, Func<TAccumulate, TSource, TAccumulate> accumulator) { _source = source; _seed = seed; _accumulator = accumulator; } protected override _ CreateSink(IObserver<TAccumulate> observer, IDisposable cancel) { return new _(_seed, _accumulator, observer, cancel); } protected override IDisposable Run(_ sink) { return ObservableExtensions.SubscribeSafe<TSource>(_source, (IObserver<TSource>)sink); } } }