1 files changed, 44 insertions, 0 deletions
diff --git a/crypto/src/util/collections/ReadOnlyCollection.cs b/crypto/src/util/collections/ReadOnlyCollection.cs
new file mode 100644
index 000000000..a44491d0b
--- /dev/null
+++ b/crypto/src/util/collections/ReadOnlyCollection.cs
@@ -0,0 +1,44 @@
+using System;
+using System.Collections.Generic;
+
+namespace Org.BouncyCastle.Utilities.Collections
+{
+    internal abstract class ReadOnlyCollection<T>
+        : ICollection<T>
+    {
+        System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator()
+        {
+            return GetEnumerator();
+        }
+
+        public bool IsReadOnly => true;
+
+        public void Add(T item) => throw new NotSupportedException();
+        public void Clear() => throw new NotSupportedException();
+        public bool Remove(T item) => throw new NotSupportedException();
+
+        public abstract bool Contains(T item);
+        public abstract int Count { get; }
+        public abstract void CopyTo(T[] array, int arrayIndex);
+        public abstract IEnumerator<T> GetEnumerator();
+    }
+
+    internal class ReadOnlyCollectionProxy<T>
+        : ReadOnlyCollection<T>
+    {
+        private readonly ICollection<T> m_target;
+
+        internal ReadOnlyCollectionProxy(ICollection<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 int Count => m_target.Count;
+        public override void CopyTo(T[] array, int arrayIndex) => m_target.CopyTo(array, arrayIndex);
+        public override IEnumerator<T> GetEnumerator() => m_target.GetEnumerator();
+    }
+}