Merging //UE4/Main/Engine/... to //UE4/Dev-Mobile

#rb None

[CL 4749281 by Jack Porter in Dev-Mobile branch]

Engine/Source/Programs/DotNETCommon/DotNETUtilities/ReadOnlyHashSet.cs

@@ -0,0 +1,95 @@
+// Copyright 1998-2019 Epic Games, Inc. All Rights Reserved.
+
+using System;
+using System.Collections;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace Tools.DotNETCommon
+{
+	/// <summary>
+	/// Wrapper around the HashSet container that only allows read operations
+	/// </summary>
+	/// <typeparam name="T">Type of element for the hashset</typeparam>
+	public class ReadOnlyHashSet<T> : IReadOnlyCollection<T>
+	{
+		/// <summary>
+		/// The mutable hashset
+		/// </summary>
+		HashSet<T> Inner;
+
+		/// <summary>
+		/// Constructor
+		/// </summary>
+		/// <param name="Inner">The mutable hashset</param>
+		public ReadOnlyHashSet(HashSet<T> Inner)
+		{
+			this.Inner = Inner;
+		}
+
+		/// <summary>
+		/// Constructor
+		/// </summary>
+		/// <param name="Collection">Elements for the hash set</param>
+		public ReadOnlyHashSet(IEnumerable<T> Elements)
+		{
+			this.Inner = new HashSet<T>(Elements);
+		}
+
+		/// <summary>
+		/// Constructor
+		/// </summary>
+		/// <param name="Collection">Elements for the hash set</param>
+		/// <param name="Comparer">Comparer for elements in the set</param>
+		public ReadOnlyHashSet(IEnumerable<T> Elements, IEqualityComparer<T> Comparer)
+		{
+			this.Inner = new HashSet<T>(Elements, Comparer);
+		}
+
+		/// <summary>
+		/// Number of elements in the set
+		/// </summary>
+		public int Count
+		{
+			get { return Inner.Count; }
+		}
+
+		/// <summary>
+		/// The comparer for elements in the set
+		/// </summary>
+		public IEqualityComparer<T> Comparer
+		{
+			get { return Inner.Comparer; }
+		}
+
+		/// <summary>
+		/// Tests whether a given item is in the set
+		/// </summary>
+		/// <param name="Item">Item to check for</param>
+		/// <returns>True if the item is in the set</returns>
+		public bool Contains(T Item)
+		{
+			return Inner.Contains(Item);
+		}
+
+		/// <summary>
+		/// Gets an enumerator for set elements
+		/// </summary>
+		/// <returns>Enumerator instance</returns>
+		public IEnumerator<T> GetEnumerator()
+		{
+			return Inner.GetEnumerator();
+		}
+
+		/// <summary>
+		/// Gets an enumerator for set elements
+		/// </summary>
+		/// <returns>Enumerator instance</returns>
+		IEnumerator IEnumerable.GetEnumerator()
+		{
+			return ((IEnumerable)Inner).GetEnumerator();
+		}
+	}
+}