Imported Upstream version 3.6.0

Former-commit-id: da6be194a6b1221998fc28233f2503bd61dd9d14

external/rx/Rx/NET/Source/System.Reactive.Linq/Reactive/Internal/Observers.cs

@@ -0,0 +1,109 @@
+// Copyright (c) Microsoft Open Technologies, Inc. All rights reserved. See License.txt in the project root for license information.
+
+namespace System.Reactive
+{
+    class NopObserver<T> : IObserver<T>
+    {
+        public static readonly IObserver<T> Instance = new NopObserver<T>();
+
+        public void OnCompleted()
+        {
+        }
+
+        public void OnError(Exception error)
+        {
+        }
+
+        public void OnNext(T value)
+        {
+        }
+    }
+
+    class DoneObserver<T> : IObserver<T>
+    {
+        public static readonly IObserver<T> Completed = new DoneObserver<T>();
+
+        public Exception Exception { get; set; }
+
+        public void OnCompleted()
+        {
+        }
+
+        public void OnError(Exception error)
+        {
+        }
+
+        public void OnNext(T value)
+        {
+        }
+    }
+
+    class DisposedObserver<T> : IObserver<T>
+    {
+        public static readonly IObserver<T> Instance = new DisposedObserver<T>();
+
+        public void OnCompleted()
+        {
+            throw new ObjectDisposedException("");
+        }
+
+        public void OnError(Exception error)
+        {
+            throw new ObjectDisposedException("");
+        }
+
+        public void OnNext(T value)
+        {
+            throw new ObjectDisposedException("");
+        }
+    }
+
+    class Observer<T> : IObserver<T>
+    {
+        private readonly ImmutableList<IObserver<T>> _observers;
+
+        public Observer(ImmutableList<IObserver<T>> observers)
+        {
+            _observers = observers;
+        }
+
+        public void OnCompleted()
+        {
+            foreach (var observer in _observers.Data)
+                observer.OnCompleted();
+        }
+
+        public void OnError(Exception error)
+        {
+            foreach (var observer in _observers.Data)
+                observer.OnError(error);
+        }
+
+        public void OnNext(T value)
+        {
+            foreach (var observer in _observers.Data)
+                observer.OnNext(value);
+        }
+
+        internal IObserver<T> Add(IObserver<T> observer)
+        {
+            return new Observer<T>(_observers.Add(observer));
+        }
+
+        internal IObserver<T> Remove(IObserver<T> observer)
+        {
+            var i = Array.IndexOf(_observers.Data, observer);
+            if (i < 0)
+                return this;
+
+            if (_observers.Data.Length == 2)
+            {
+                return _observers.Data[1 - i];
+            }
+            else
+            {
+                return new Observer<T>(_observers.Remove(observer));
+            }
+        }
+    }
+}