namespace System.Reactive.Linq.ObservableImpl { internal sealed class Aggregate<TSource, TAccumulate> : Producer<TAccumulate, Aggregate<TSource, TAccumulate>._> { internal sealed class _ : Sink<TSource, TAccumulate> { private readonly Func<TAccumulate, TSource, TAccumulate> _accumulator; private TAccumulate _accumulation; public _(TAccumulate seed, Func<TAccumulate, TSource, TAccumulate> accumulator, IObserver<TAccumulate> observer) : base(observer) { _accumulator = accumulator; _accumulation = seed; } public override void OnNext(TSource value) { try { _accumulation = _accumulator(_accumulation, value); } catch (Exception error) { _accumulation = default(TAccumulate); ForwardOnError(error); } } public override void OnError(Exception error) { _accumulation = default(TAccumulate); ForwardOnError(error); } public override void OnCompleted() { TAccumulate accumulation = _accumulation; _accumulation = default(TAccumulate); ForwardOnNext(accumulation); ForwardOnCompleted(); } } 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) { return new _(_seed, _accumulator, observer); } protected override void Run(_ sink) { sink.Run(_source); } } }