Imported Upstream version 4.6.0.125

Former-commit-id: a2155e9bd80020e49e72e86c44da02a8ac0e57a4

mcs/class/referencesource/System.IdentityModel/System/IdentityModel/ImmutableCollection.cs

@@ -0,0 +1,74 @@
+//----------------------------------------------------------
+// Copyright (c) Microsoft Corporation.  All rights reserved.
+//------------------------------------------------------------
+
+namespace System.IdentityModel
+{
+    using System;
+    using System.Collections;
+    using System.Collections.Generic;
+    using System.Collections.ObjectModel;
+
+    //
+    // A collection that can be made immutable by calling the
+    // MakeReadOnly method. Once the collection is made read-only
+    // Add, Remove and Clear methods will throw an exception 
+    // failing to add a item to the collection.
+    //
+    internal sealed class ImmutableCollection<T> : Collection<T>, IList<T>, IList
+    {
+        bool isReadOnly = false;
+
+        public void MakeReadOnly()
+        {
+            this.isReadOnly = true;
+        }
+
+        public bool IsReadOnly
+        {
+            get { return this.isReadOnly; }
+        }
+
+        protected override void ClearItems()
+        {
+            if (this.isReadOnly)
+                throw DiagnosticUtility.ExceptionUtility.ThrowHelperError(new InvalidOperationException(SR.GetString(SR.ObjectIsReadOnly)));
+
+            base.ClearItems();
+        }
+
+        protected override void InsertItem(int index, T item)
+        {
+            if (this.isReadOnly)
+                throw DiagnosticUtility.ExceptionUtility.ThrowHelperError(new InvalidOperationException(SR.GetString(SR.ObjectIsReadOnly)));
+
+            base.InsertItem(index, item);
+        }
+
+        protected override void RemoveItem(int index)
+        {
+            if (this.isReadOnly)
+                throw DiagnosticUtility.ExceptionUtility.ThrowHelperError(new InvalidOperationException(SR.GetString(SR.ObjectIsReadOnly)));
+
+            base.RemoveItem(index);
+        }
+
+        protected override void SetItem(int index, T item)
+        {
+            if (this.isReadOnly)
+                throw DiagnosticUtility.ExceptionUtility.ThrowHelperError(new InvalidOperationException(SR.GetString(SR.ObjectIsReadOnly)));
+
+            base.SetItem(index, item);
+        }
+
+        bool ICollection<T>.IsReadOnly
+        {
+            get { return this.isReadOnly; }
+        }
+
+        bool IList.IsReadOnly
+        {
+            get { return this.isReadOnly; }
+        }
+    }
+}