1 files changed, 61 insertions, 0 deletions
diff --git a/crypto/src/util/collections/ReadOnlySet.cs b/crypto/src/util/collections/ReadOnlySet.cs
new file mode 100644
index 000000000..36c198f07
--- /dev/null
+++ b/crypto/src/util/collections/ReadOnlySet.cs
@@ -0,0 +1,61 @@
+using System;
+using System.Collections.Generic;
+
+namespace Org.BouncyCastle.Utilities.Collections
+{
+    internal abstract class ReadOnlySet<T>
+        : ISet<T>
+    {
+        System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator()
+        {
+            return GetEnumerator();
+        }
+
+        public bool IsReadOnly => true;
+
+        void ICollection<T>.Add(T item) => throw new NotSupportedException();
+
+        public bool Add(T item) => throw new NotSupportedException();
+        public void Clear() => throw new NotSupportedException();
+        public void ExceptWith(IEnumerable<T> other) => throw new NotSupportedException();
+        public void IntersectWith(IEnumerable<T> other) => throw new NotSupportedException();
+        public bool Remove(T item) => throw new NotSupportedException();
+        public bool SetEquals(IEnumerable<T> other) => throw new NotSupportedException();
+        public void SymmetricExceptWith(IEnumerable<T> other) => throw new NotSupportedException();
+        public void UnionWith(IEnumerable<T> other) => throw new NotSupportedException();
+
+        public abstract bool Contains(T item);
+        public abstract void CopyTo(T[] array, int arrayIndex);
+        public abstract int Count { get; }
+        public abstract IEnumerator<T> GetEnumerator();
+        public abstract bool IsProperSubsetOf(IEnumerable<T> other);
+        public abstract bool IsProperSupersetOf(IEnumerable<T> other);
+        public abstract bool IsSubsetOf(IEnumerable<T> other);
+        public abstract bool IsSupersetOf(IEnumerable<T> other);
+        public abstract bool Overlaps(IEnumerable<T> other);
+    }
+
+    internal class ReadOnlySetProxy<T>
+        : ReadOnlySet<T>
+    {
+        private readonly ISet<T> m_target;
+
+        internal ReadOnlySetProxy(ISet<T> target)
+        {
+            if (target == null)
+                throw new ArgumentNullException(nameof(target));
+
+            m_target = target;
+        }
+
+        public override bool Contains(T item) => m_target.Contains(item);
+        public override void CopyTo(T[] array, int arrayIndex) => m_target.CopyTo(array, arrayIndex);
+        public override int Count => m_target.Count;
+        public override IEnumerator<T> GetEnumerator() => m_target.GetEnumerator();
+        public override bool IsProperSubsetOf(IEnumerable<T> other) => m_target.IsProperSubsetOf(other);
+        public override bool IsProperSupersetOf(IEnumerable<T> other) => m_target.IsProperSupersetOf(other);
+        public override bool IsSubsetOf(IEnumerable<T> other) => m_target.IsSubsetOf(other);
+        public override bool IsSupersetOf(IEnumerable<T> other) => m_target.IsSupersetOf(other);
+        public override bool Overlaps(IEnumerable<T> other) => m_target.Overlaps(other);
+    }
+}