Polish ReadOnlyHashSet

 * Fix compiler break in ReadOnlyHashSet.
 * Add a bit of documentation.
 * Hide the ICollection<T> members that aren't supported via explicit interface implementation.

Author: Robert El-Soudani

Assets/HoloToolkit/Utilities/Scripts/ReadOnlyHashSet.cs

@@ -1,13 +1,18 @@
 // Copyright (c) Microsoft Corporation. All rights reserved.
 // Licensed under the MIT License. See LICENSE in the project root for license information.
 
-using HoloToolkit.Diagnostics;
 using System;
 using System.Collections;
 using System.Collections.Generic;
+using UnityEngine;
 
 namespace HoloToolkit.Unity
 {
+    /// <summary>
+    /// A wrapper for <see cref="HashSet{T}"/> that doesn't allow modification of the set. This is
+    /// useful for handing out references to a set that is going to be modified internally, without
+    /// giving external consumers the opportunity to accidentally modify the set.
+    /// </summary>
     public class ReadOnlyHashSet<TElement> :
         ICollection<TElement>,
         IEnumerable<TElement>,
@@ -17,7 +22,7 @@ public class ReadOnlyHashSet<TElement> :
 
         public ReadOnlyHashSet(HashSet<TElement> underlyingSet)
         {
-            Assert.IsTrue(DiagnosticContext.Create(), underlyingSet != null, "underlyingSet cannot be null.");
+            Debug.Assert(underlyingSet != null, "underlyingSet cannot be null.");
 
             this.underlyingSet = underlyingSet;
         }
@@ -27,17 +32,17 @@ public int Count
             get { return underlyingSet.Count; }
         }
 
-        public bool IsReadOnly
+        bool ICollection<TElement>.IsReadOnly
         {
             get { return true; }
         }
 
-        public void Add(TElement item)
+        void ICollection<TElement>.Add(TElement item)
         {
             throw NewWriteDeniedException();
         }
 
-        public void Clear()
+        void ICollection<TElement>.Clear()
         {
             throw NewWriteDeniedException();
         }
@@ -57,7 +62,7 @@ public IEnumerator<TElement> GetEnumerator()
             return underlyingSet.GetEnumerator();
         }
 
-        public bool Remove(TElement item)
+        bool ICollection<TElement>.Remove(TElement item)
         {
             throw NewWriteDeniedException();
         }