1 files changed, 59 insertions, 0 deletions
diff --git a/src/mscorlib/src/System/Collections/Generic/IReadOnlyCollection.cs b/src/mscorlib/src/System/Collections/Generic/IReadOnlyCollection.cs
new file mode 100644
index 0000000000..e9d86518ac
--- /dev/null
+++ b/src/mscorlib/src/System/Collections/Generic/IReadOnlyCollection.cs
@@ -0,0 +1,59 @@
+// Copyright (c) Microsoft. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+/*============================================================
+**
+** Interface:  IReadOnlyCollection<T>
+** 
+** 
+**
+** Purpose: Base interface for read-only generic lists.
+** 
+===========================================================*/
+using System;
+using System.Diagnostics.Contracts;
+using System.Runtime.CompilerServices;
+
+namespace System.Collections.Generic
+{
+
+    // Provides a read-only, covariant view of a generic list.
+
+    // Note that T[] : IReadOnlyList<T>, and we want to ensure that if you use
+    // IList<YourValueType>, we ensure a YourValueType[] can be used 
+    // without jitting.  Hence the TypeDependencyAttribute on SZArrayHelper.
+    // This is a special workaround internally though - see VM\compile.cpp.
+    // The same attribute is on IList<T>, IEnumerable<T>, ICollection<T>, and IReadOnlyList<T>.
+    [TypeDependencyAttribute("System.SZArrayHelper")]
+#if CONTRACTS_FULL
+    [ContractClass(typeof(IReadOnlyCollectionContract<>))]
+#endif
+    // If we ever implement more interfaces on IReadOnlyCollection, we should also update RuntimeTypeCache.PopulateInterfaces() in rttype.cs
+    public interface IReadOnlyCollection<out T> : IEnumerable<T>
+    {
+        int Count { get; }
+    }
+
+#if CONTRACTS_FULL
+    [ContractClassFor(typeof(IReadOnlyCollection<>))]
+    internal abstract class IReadOnlyCollectionContract<T> : IReadOnlyCollection<T>
+    {
+        int IReadOnlyCollection<T>.Count {
+            get {
+                Contract.Ensures(Contract.Result<int>() >= 0);
+                return default(int);
+            }
+        }
+
+        IEnumerator<T> IEnumerable<T>.GetEnumerator()
+        {
+            return default(IEnumerator<T>);
+        }
+
+        IEnumerator IEnumerable.GetEnumerator()
+        {
+            return default(IEnumerator);
+        }
+    }
+#endif
+}