reactive/Rx.NET/Source/src/System.Reactive/Linq/Observable/Select.cs

// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the Apache 2.0 License.
// See the LICENSE file in the project root for more information. 

namespace System.Reactive.Linq.ObservableImpl
{
    internal static class Select<TSource, TResult>
    {
        internal sealed class Selector : Producer<TResult>
        {
            private readonly IObservable<TSource> _source;
            private readonly Func<TSource, TResult> _selector;

            public Selector(IObservable<TSource> source, Func<TSource, TResult> selector)
            {
                _source = source;
                _selector = selector;
            }

            protected override IDisposable CreateSink(IObserver<TResult> observer, IDisposable cancel) => new _(_selector, observer, cancel);

            protected override IDisposable Run(IObserver<TResult> observer, IDisposable cancel, Action<IDisposable> setSink)
            {
                var sink = new _(_selector, observer, cancel);
                setSink(sink);
                return _source.SubscribeSafe(sink);
            }

            private sealed class _ : Sink<TResult>, IObserver<TSource>
            {
                private readonly Func<TSource, TResult> _selector;

                public _(Func<TSource, TResult> selector, IObserver<TResult> observer, IDisposable cancel)
                    : base(observer, cancel)
                {
                    _selector = selector;
                }

                public void OnNext(TSource value)
                {
                    var result = default(TResult);
                    try
                    {
                        result = _selector(value);
                    }
                    catch (Exception exception)
                    {
                        base._observer.OnError(exception);
                        base.Dispose();
                        return;
                    }

                    base._observer.OnNext(result);
                }

                public void OnError(Exception error)
                {
                    base._observer.OnError(error);
                    base.Dispose();
                }

                public void OnCompleted()
                {
                    base._observer.OnCompleted();
                    base.Dispose();
                }
            }
        }

        internal sealed class SelectorIndexed : Producer<TResult>
        {
            private readonly IObservable<TSource> _source;
            private readonly Func<TSource, int, TResult> _selector;

            public SelectorIndexed(IObservable<TSource> source, Func<TSource, int, TResult> selector)
            {
                _source = source;
                _selector = selector;
            }

            protected override IDisposable CreateSink(IObserver<TResult> observer, IDisposable cancel) => new _(_selector, observer, cancel);

            protected override IDisposable Run(IObserver<TResult> observer, IDisposable cancel, Action<IDisposable> setSink)
            {
                var sink = new _(_selector, observer, cancel);
                setSink(sink);
                return _source.SubscribeSafe(sink);
            }

            private sealed class _ : Sink<TResult>, IObserver<TSource>
            {
                private readonly Func<TSource, int, TResult> _selector;
                private int _index;

                public _(Func<TSource, int, TResult> selector, IObserver<TResult> observer, IDisposable cancel)
                    : base(observer, cancel)
                {
                    _selector = selector;
                    _index = 0;
                }

                public void OnNext(TSource value)
                {
                    var result = default(TResult);
                    try
                    {
                        result = _selector(value, checked(_index++));
                    }
                    catch (Exception exception)
                    {
                        base._observer.OnError(exception);
                        base.Dispose();
                        return;
                    }

                    base._observer.OnNext(result);
                }

                public void OnError(Exception error)
                {
                    base._observer.OnError(error);
                    base.Dispose();
                }

                public void OnCompleted()
                {
                    base._observer.OnCompleted();
                    base.Dispose();
                }
            }
        }
    }
}